#Lp I ' j "->ir.ii:Ti^.< ~-^r*~ ~~^; -.-.-.; PreserLteci "by MISS CATHARINE LAV'OLFE. v5f i nj j- a 3~ _D CD m o A HISTORY OF THE BRITISH MARINE TESTACEOUS MOLLUSCA, DISTRIBUTED IN THEIR NATURAL ORDER. o / MOLLUSC A TEST ACE A MARIUM BRITANNICORUM, A HISTORY OF THE BRITISH MARINE TESTACEOUS MOLLUSCA, DISTRIBUTED IN THEIR NATURAL ORDER, ON THE BASIS OF THE ORGANIZATION OF THE ANIMALS ; WITH REFERENCES AND NOTES ON EVERY BRITISH SPECIES. BY WILLIAM CLARK. LONDON: JOHN VAN VOORST, PATERNOSTER ROW. M.DCCC.LV. PRINTED BY TAYLOR AND FRANCIS, BED LION COURT, FLEET STREET. FLAM, MAM. TO THE INHABITANTS OF EXMOUTH, IX TESTIMONY OF HIS SINCERE WISHES FOR THEIR WELFARE, AND FOR THE PROSPERITY OF THEIR TOWN ; * AND ALSO IN ACKNOWLEDGMENT OF THE UNVARIED KINDNESS WHICH THEY HAVE EXHIBITED TOWARDS THE AUTHOR AND HIS FAMILY IN THEIR VISITS TO THAT LOVELY LOCALITY DURING THE LONG PERIOD OF FORTY-FIVE YEARS, THIS VOLUME IS RESPECTFULLY DEDICATED. PREFACE. IT has long been the fashion to present the reader with a prologue ; which, however, I have observed, of late years, has become shorter and shorter. The utility of this practice is questionable, as the body of the work includes all that can be said in a preface, and by it we forestall the pleasures of expectation ; besides, be it good or bad and the author is frequently not the writer it often unjustly decides the fate of a book, causing a bad one to be read, or a good one to be thrown aside ; nevertheless I have in some measure complied with an old custom, by giving a few prelimi- nary remarks in the introduction to the classification. It will be observed that some of the families and genera of the Cephalopoda and Pulmonifera have been admitted into the sketch of the classification to com- plete the chain of the Molluscan series ; to enter on their consideration forms no part of the plan of this work, which relates exclusively to the British Marine Testaceous Mollusca. In some instances " nobis " is attached to the name of well-known species ; this has been done, not from any desire to assume credit for the labours and disco- viii PREFACE. veries of others, but simply to markeither that we have made some alteration in the nomenclature of the species, or that we have included under the name forms hitherto regarded as distinct. Many of the memoirs have been admitted into the ' Annals of Natural History,' but as it would occupy about four years to have the remainder of them inserted in that excellent work, I have determined to print the whole at once in a collective form, and the Editors of the ' Annals ' have liberally accorded me permission to reprint those which have appeared in the pages of their journal. My reason for making this arrangement is, that, at my age, it would be almost presumptuous in me to calculate upon being able to watch the publi- cation of my observations during such a long period as four years. I can entertain no doubt that my work is very de- fective, and, on such a subject, it would still be so, if I were to bestow the labour of another half century upon it. Were it at all probable that I might re- examine the whole matter, with the advantage of having first impressions defined and corrected by intermediate study, I should probably not have chosen this desultory form of publication ; but if any justification of such a course be required, I have at least the opinion of Pro- fessor James Forbes to support me. That eminent philosopher, in his excellent ' History of Norway and its Glaciers,' well observes, "But a pretty long experience in such matters has convinced me that they act wisely and well, who, having used their opportunities to the best of their power, PEEFACE. ix communicate the results of their observations to the world without waiting for a period (never perhaps to arrive) when they may themselves have the credit of completing and perfecting them. It is better, whilst the freshness of recollection is undinimed, and the mind is in a position to draw a correct parallel between older and quite recent observations, and thus to give our descriptions the necessary development, to throw into them whatever there may be of value in our peculiar experience or habits of investigation, and frankly to invite our fellow-labourers to do in our stead what we would gladly have done but for some inevitable want of health, leisure, or opportunity. Were this course more generally followed in the sciences, both of obser- vation and experiment, I am persuaded that by grasping at less we should attain more even in personal repu- tation and should unquestionably advance the interests of knowledge." Norfolk Crescent, Bath, November, 1854. TABLE OF CONTENTS. PAGE SYNOPSIS OF THE CLASSIFICATION 4 ACEPHALA 20 SPECIFIC DESCRIPTIONS OF THE ACEPHALA 35 GASTEROPODA 225 SPECIFIC DESCRIPTIONS OF THE GASTEROPODA 226 LlST OF THE EXOTIC SPECIES THAT HAVE BEEN IMPROPERLY ADMITTED INTO THE BRITISH LIST 509 APPENDIX 511 INDEX . . 529 ERRATA, CORRIGENDA ET ADDENDA. Page 16, line 5, for and term read and term one of. 36, 19, J- read -^ to ^. 42, ,, 19, 20, for the A. sfriata, which is the A. patelliformis, read the A.striata, which is a mere form of the A. patelliformis. ,, 54, ,, 35, for Lima subauriculatus read Lima subauriculata. ,, 123, ,, 11, rectum read intestine. ,, 128, ,, 30, 31, for BRTMACULATA read BIMACULATA. ,, 131, 1, for the branchial artery read the branchial artery or vein. ,, 135, 28, as it has many features of the Myadce and AnatinidoR, read as some authors say it has many features of the Myadce. 168, 10, Having written to Professor Ed. Forbes in Feb. 1849, on what I conceived to be the improper association of Lutraria with the Mactridat instead of being placed with the Myadee, he replied thus :- 4 . Craig>s Court> Feb fi> Ig49< " My dear Sir, 1 quite agree in all you say about Lutraria, and shall keep your letter for the Appendix. So entirely did I agree in the view you take, that I sent the MS. to he printed with the Myadce. The printers, however, mis- laid it, and I was forced to put it in the old place. " Believe me, dear Sir, with many thanks, " Most sincerely yours, " W m Clark, Esq." " EDWARD FORBES." ,, 246, 31, for in the Articulata read in the annelidan Articulata. 247, ,, 17, van read rear. 296, ,, 31, ,, Chemnitzida read Chemnitziw. 310, 20, branded read brindled. ,, 331, ,, 16, ,, tenebra read terebra. 444, ,, 22, 23, Dele the words " the cause has perhaps been its anomalous aspect." BRITISH MARINE TESTACEOUS MOLLUSCA. CLASSIFICATION. IT will be convenient, with reference to this work on the British Marine Testaceous Mollusca*, that a synopsis of the classification of the whole tribe should be submitted, accom- panied by a short analysis, that the incidents and position of any particular family may at once be examined. Most naturalists have their own plan of distribution with respect to natural order ; perhaps, then, I shall not incur the imputation of an unmeasured presumption, if I venture to offer a sketch of mine, founded on forty years' sedulous investigation of our indigena. I have not the vanity to suppose that my scheme is superior to the methods of my brethren ; but it is novel, and exhibits, as I think, a progressive advancement of animal organization and harmony of arrangement from the beginning of the class to its termination, by which groups of similar affinities are insensibly united as far as is possible, and suc- ceed each other, on the basis of external and internal anato- mical considerations. These memoirs are the result of numerous visits to the * The main object of this work is the description of the animals of the British marine testaceous Mollusca, and though a few of the freshwater and land families and genera are mentioned, it is only incidentally, and to fill up the outline of the British classification, but no account of their species will be given. B 2 BEITISH MARINE TESTACEOUS MOLLUSCA: South Devon coast at Exmouth, where I have passed my leisure in the dissection and examination of the Marine Tes- taceous Mollusca. Nearly every animal has undergone, in a living state, my personal examination, and in many species often repeated. I have had my own dredger, and I may say with some confidence, that there are few individuals who have had better opportunities of observing the organs, their functions, and the habitudes of these varied and interesting animals, than myself. I trust that my dissections and in- vestigations will give such a general, and in some measure particular account of their external configuration and internal anatomy as will suffice to furnish the younger students of this branch of zoology with some knowledge of their organization, and afford them sufficient aid to discriminate the organs of the animals, so as to let none pass without careful observation ; for how many curious creatures, which perhaps only occur once in a lifetime, have been overlooked for want of such assistance, and are for an indefinite time lost to science ! I speak with deep regret on this point ; as in my earlier career I have neglected opportunities that have never occurred since, and which I have felt the loss of. The anatomies of Pholas dactylus, Teredo megotara, Denta- lium tarentinum, Bulla hydatis, and other desultory anatomical observations by myself, with references to M. Cuvier, the " principium et fons" of faithful comparative anatomy, will sufficiently explain the structure of the Acephala and Gastero- poda that have been treated of in these memoirs ; which are by no means to be considered as strictly local ones. Though the species have been obtained from one vicinity, they will be found to give, I hope, a faithful portraiture of most of the animals of the entire class of the British marine testaceous Mollusca. There are, however, gaps which it has never been in the power of malacologists to fill up ; but the hope of acquiring the rare desiderata ought not to be considered as forlorn. I have lately fallen in with very unexpected acquisitions which afford a practical illustration of the quotation " Turne, quod optanti Divum promittere nemo Auderet, volvenda dies, en! attulit ultro." CLASSIFICATION. 3 I may mention that these remarks were scarcely dry, when I received from Exmouth a pine log full of magnificent Teredo megotara alive, which species I had not seen for thirty years, and enabled me to supply the anatomy of the Teredines. And in 1852 I reaped a splendid crop of rare desiderata, which I had almost despaired of. The gleanings of the harvest still remain, and will amply repay the labours of the energetic naturalist. We have given no figures of the animals or shells, and only occasionally in the text, short notices of the hard parts ; but we have supplied this want, by referring to the excellent and recently published 'British Mollusca/ by Professor Forbes and Mr. Hanley, of which we will observe, that no mala- cologist can dispense with this vade mecum, wherein will be found delineations, and copious descriptions of the shells of every animal mentioned in our work, with figures of many typical animals, and we have added references to those British species that have escaped our researches. Sir Walter Scott tells us, that nature having denied Mr. Croftangry a pencil, he endeavoured to make words answer the purpose of delinea- tion ; I almost think, though fancy may be equally expansive in both cases, that if one has any general knowledge of the subject, a particular description of any of the variously formed objects of nature would ensure as good a distinctive resem- blance as if drawn pictorially from life ; the only exception is the human race, in which nature having arrived at the ex- treme limits of animal composition, illustrated by there being absolutely the same number and quality of the external organs in every tribe, the chef-d'oeuvre of her works may, perhaps, be better expressed by portrait than by description ; but all the other objects of animated nature, even in the same divi- sion, differ so exceedingly from each other, for example, in the present case, the Mollusca, that descriptive notes may possibly be preferable to artistical representation. B 2 4 BEITISH MARINE TESTACEOUS MOLLUSCA : SYNOPSIS OF THE FAMILIES AND GENERA OF THE BRITISH TES- TACEOUS ACEPHALA, GASTEROPODA, AND CEPHALOPODA, DISTRIBUTED IN SIX DIVISIONS, ON THE BASES OF SEXUAL ORGANIZATION. First Division. ACEPHALA PALLIOBRANCHIATA. Hermaphrodita, sine concubitu. TEREBRATULID.E Hypothyris. Terebratula. Argiope. CRANIAD^E Crania. Second Division. ACEPHALA LAMELLIBRANCHIATA. Hermaphrodita, sine concubitu. * Mantle open, no tubes. ANOMIAD.E Anomia. PECTINID.E Pecten. OSTREAD.E Ostrea. ** Mantle open, no siphonal tubes or sessile. MYTILID.E Mytilus. Dreissena. Modiola. Crenella. Pinna. Avicula. UNIONID.E Unio. Anodon. *** Mantle open, tubes sessile or short. ARCADE Area. Pectunculus. Nucula. Leda. Galeomma. Lepton. CLASSIFICATION. LUCINID^E ........................ Lucina. KELLIADVE ........................ Kellia. MONTACUTIDJE .................... Montacuta. TURTONIAD^E .................... Turtonia. CYCLADID^E ...................... Cyclas. Pisidium. **** Mantle open, tubes short. CARDIAD.E ........................ Cardium. MACTRID.E ...................... Mactra. CYPRINID.E ...................... Cyprina. Circe. Astarte. j*. Isocardia. VENERID.-E ...................... Venus. Pullastra. DONACIDJS ........................ Donax. Ervilia. ***** Mantle open, tubes long. TELLINID.E ...................... Tellina. Syndosmya. Scrobicularia. Lucinopsis. ****** Mantle closed, tubes short. ANATINID.E ...................... Anatina. CORBULID.E ...................... Corbula. Sphsenia. Pandora. Solen. ******* Mantle closed, tubes long. SOLENID.E ........................ Solenicurtus. GASTROCH^ENID^; .................. Gastrochsena. Saxicava. Venerirupis. MYAD^: .......................... Mya. Panopsea. PHOLADID.E ...................... Pholas. Teredo. Xylophaga. BRITISH MARINE TESTACEOUS MOLLUSCA: Third Division. fLATERIBRANCHIATA. GASTEROPODA^ CYCLOBRANCHIATA. LCERVICOBRANCHIATA. Hermaphrodita, sine congressu. * Lateribranchiata. DENTALIAD^E Deiitalium. ** Cyclobranchiata. CHITONID^E Chiton. *** Cervicobranchiata. PATELLID^E Patella. Acmsea. Pileopsis. Calyptrsea. Emarginula. Fissurella. Puncturella. Haliotis. Fourth Division. GASTEROPODA of the vertebrate animals, I instance the powers and loco- motion of the Cephalopoda. In conclusion we observe, that Nature has put a veto on any arrangement that shall be exempt from anomalies and incongruities ; we must look at her largely as a class, with a few well-marked divisions, and not be too sensitive about Utopian details of strict natural order. We are prepared to expect that the present scheme will follow the fate of every other system of classification that has preceded it, however great may be the authorities from which they have sprung. It is universally admitted that the most accredited plans are unsatisfactory, and I venture to predict, that to the end of time our successors will make the same remarks. Mathema- tical nature is not an attribute of this sphere ; the votaries of that condition must seek for it " extra flammantia mcenia jmmcli." The synopsis of the genera, we again impress it, shows the impossibility of such an arrangement. We have here perhaps as much connective harmony as the Mollusca can receive. We do not say that there may not be transpositions and cer- tain modifications of the genera to meet the particular views of malacologists, but the general outline may perhaps be as near the truth as the subject will admit of. If zoologists demand a natural line, they cannot have it without excluding from the grand main various families. In consequence, our classification, at certain points, presents incongruities that no art can arrange satisfactorily, but they are brought as near to each other as Nature will allow of. We must submit, as we cannot alter her laws and dispositions. The fact of our line not according a direct totality of strict affinities, proves that Nature cannot be thus arranged, because the Supreme Creator, w r hose handmaiden she is, has not invested her with the power of effecting a symmetry beyond what she has accomplished. c 2 20 BRITISH MARINE TESTACEOUS MOLLTJSCA : ACEPHALA PALLIOBKANCHIATA. A few general remarks on the Palliobranchiate Mollusca, in addition to those in the synopsis of my classification, will be a useful reference in respect of this class of acephalous animals. I include in the general matter on the Pallio- branchiate Mollusca, the meagre notices and references to the very few recent species of this tribe that now exist; these, however, contain all that is known of the organization of this numerous group of one of the epochs which preceded that in which our orb has been described as "rudis indigestaque moles." For the reasons stated in the analysis of the Mol- lusca, I have reversed the position of this section of the bivalves, and made it the alpha instead of the omega of the Acephala. These animals derive their appellation from the respiratory apparatus forming a vascular network on the substance of the mantle, instead of being provided with the distinct sym- metrical, usually double laminse, on each side of the body of the Lamellibranchiata ; they are the Brachiopoda of Lamarck, and form two families in respect to the British iudigena, the Terebratulidce, containing tliree genera and four species, and the Craniadae, with oidy one genus and one species. This class of Acephala formed the great mass of the Mol- lusca in the palseozoic ages, as is proved by the almost infinite variety of their fossils, which are more numerous than all the other groups of Mollusca united. But in these latter days it would appear, from the excessive rarity of living species, that the race has nearly become extinct, or live in unapproachable depths ; I believe that not half a dozen species have ever been examined, and we can scarcely hope that several anomalies in the structure of these animals and their shells will ever be explained; 110 comparison can be made the same animal must be observed. The British collector cannot hope to pos- sess more than five recent species, two of which, the Hypothyris psittacea and Terebratula cranium, may be considered almost ACEPHALA PALLIOBRANCHIATA. 21 beyond acquisition ; the only chance is, that a fortunate hit may be made, and these rare productions brought to light from the deep sea beds. That the animals of this tribe are of inferior organization to the lamellibranchiate bivalves, is, I think, shown by their invariable fixity of habitat. By-the-by, it is said that in this family, and also in the Ostreadee, the sexes are distinct : if this be so, how can the genial influences pass ? for we must pre- sume some sort of coiigression. Is it contended that the germs of vitality are committed, at hap-hazard, to the waves ? I cannot concur in this doctrine. I believe all the bivalves are strict hermaphrodites, that is, without coiigression, and contain within themselves the elements of bisexuality. I return from this digression to make a few more observa- tions on the value of the palliobranchiate organization. In addition to the fixed state, it may be added, that in it the circulation is more simple, the motive power consisting only of an auricle on each side, without a ventricle. The spiral ciliated arms, though not articulated, in consequence of their hollow structure producing an equivalent flexibility, are to me sufficient evidence of an alliance with the Cirripoda ; and I think the structure of the respiratory apparatus equally con- clusive that these animals are closely related to the Ascidice. Let us examine the upper valve of Crania, fixed as it is to the animal only by muscles. I can consider it in no other light than as the analogue of the operculum of the Balani, for the protection of the animal, and support and regulation of the issue of the long, spirally-coiled, ciliated, tentacular buccal appendages ; and I think that the longer or shorter internal opercida of the Balani, which are imbedded, with a limited movement, in a cartilaginous mass, are only tantamount to the internal apophysary processes of such of the Pallio- branchiata as have them ; and for those which are destitute of these peculiar supports, the issue of the long spiral arms is regulated, as in the pedunculated Cirripoda, which have not the moveable opercula of the Balani. The spiral arms in both species of Balani, as well as in the Brachiopoda, besides tenta- cular and buccal functions, may also serve as the muscular 22 BRITISH MARINE TESTACEOUS MOLLTJSCA: agents for the opening and closure of the valves, in aid of other special muscles. It may be said that these views are far-fetched, or imagi- nary; but if naturalists would seriously consider that the oper- culum of the Balani is of the nature of an apophysis for a particular purpose, they can only come to the conclusion that such an appendage can have no other use but for the support, issue, and regulation of the buccal tentacular arms. If it is asked, what is the use of the apophyses of the Palliobranchiata? the same answer only can be given. These subunibonal blades appear in the Pholades and Teredines ; their use is the same as the processes in the Palliobranchiata, and the opercula of the Cirripoda, for the support and regulation of certain organs of the animal. With the exception of the genus Hypothyris, the shells of these animals are invariably covered with punctures or fora- mina, which would appear to give them a slight cross with still inferior classes. There is nothing peculiar in the repro- ductive organs ; a similar disposition of them is seen on the mantle of Anomia and in some of the Pectines. In this group the animal is deposited in its shell differently from the Lamel- libranchiata ; the larger or convex valve, though uppermost, is really, with respect to the animal, the dorsal one, and the under valve the ventral one ; an approach to a similar position of the animal may be observed in Anomia, Pecten and Ostrea. In the Palliobranchiata the nervous system is more sparingly developed; they have lost the knotted spinal cord of their remoter relatives, the Cirripoda, which in them is disposed in detached ganglions, the result of the change they have under- gone in the plan of their organization; and for the same reason, the articulation of the spiral arms has disappeared, and is replaced by their tubular flexibility, the use and form of the organs still remaining the same in them as in the Cirripoda. I think enough has been said to show that the pallio- branchiate bivalves are of inferior organic structure to that of the lamellibranchiate Acephala. We refer those who are desirous to be informed of what is known of the organization ACEPHALA LAMELLIBEANCHIATA. 23 of this interesting and almost undeveloped class, to Professor Owen's Memoir, vol. i. of the ' Zoological Transactions/ and to M. Deshayes and Milne-Edwards's comment and observa- tions, vol. vii. p. 305-329 of their second edition of Lamarck's 1 Animaux sans Vertebres/ We conclude by repeating our opinion that the Pallio- branchiata are not of co-ordinate organization with the Lamel- libraiichiata, but an inferior group, having many connective links with the Cirripoda. Our notes are unavoidably scanty, from the dearth of materials and difficulty of the subject. We have done : as facts cannot be stated, hypothesis ought not to supply their place. ACEPHALA LAMELLIBRANCHIATA. I shall now give an outline of the anatomy of the lamelli- branchiate bivalves, to serve as a standard of comparison. The internal structure of the animals of this division is less complicated than in the Gasteropoda, and presents such a similarity throughout the whole class, as to render it unne- cessary to give more than a detailed account of the organs and functions of the animals, without reference to a particular species. This generalization will include all the genera of the subsequent groups of the Acephala that may be noticed, except that especial care will be had to note any essential departure from the general organization in any particular genus or species. The circulation, including the respiration, is complete ; it usually consists of a pair, of infinite variety of outline, of suboval vascular plates, fixed under the mantle on each side the body ; these are composed of a network of branchial tubes, and are each furnished with an arterial and branchial vein, the one to receive the blood from the vense cavse for aeration, and the other to convey it through the auricles to the heart, to be again transmitted into the system ; the artery of each lamina is situate at the upper margins of the branchiae, at 24 BEITISH MARINE TESTACEOUS MOLLUSCA : their junction with the body, under the mantle, at the dorsal range, and is of concurrent length with them ; each branchial vein coasts the margins of its respective lamina. The motive power of the circulation is a heart, which is a simple ventricle, and two symmetrical, oblong auricles, one on each side of it ; it is placed subcentrally on the dorsal range, rather nearer to the posterior half, and with the auricles embraces the rectum or intestine, which thus apparently passes through it. But this is not the case with every bivalve, though the major part of them are thus constituted ; the Ostrece, Area, and some few others are exceptions. The heart and auricles are nearly pellucid, of the thinnest texture, and apparently of feeble power; the auricles have valves to prevent a reflux of the blood ; they are usually situate at their junction with the heart, sometimes at the point where the branchial veins unite Avith them, and they sometimes are found at both contacts. The inspirations and expirations are each about seven or eight in a minute. The heart gives forth at least two aortic branches, which ramifying furnish arteries to the system, and at their invisible termini the venous reflux has its origin, and by continual anastomoses and inosculations, in their progress to the arterial centre, terminate in one or more trunk veins or vense cavse, which effect a coalition with the branchial artery. Though the circulation is what is called complete, it may be liable to interruptions, divergences and retardations ; that is, if the opinion of some zoologists, Mr. Garner amongst them, is well founded, that the whole of the blood is not returned to the body in each circulation, and a part of it, from various organs, passes to a set of veins which are concentrated ante- riorly, on each side the dorsal range, in an elongated sinus, extending to and under the pericardium ; and that these veins, by small lateral internal sacs, ducts or orifices, pass the secre- tions, or fluids they have distilled, to the mantle, in aid of structure and coloration, for the use of the ova and other organs ; and that branches from this fasciculus of veins, after the depuration of their contents, transmit the blood into the branchial artery ; it is also said that other portions of the ACEPHALA LAMELLIBKANCHIATA. 25 venous blood enter by branches into the principal branchial vein and auricles, and is sent into the circulation without being transmitted to the branchiae for aeration. Part of these views I can confirm, as far as relates to the spongy excretory glands at the anterior end of the sinus above alluded to ; they are visible in Pholas dactyhis, and conspicuously in P. parva ; their uses are fully described under the title of excretory organs of P. dactylus. As to a portion of the blood being returned to the heart without receiving the dose of oxygen, I have not had it in my power to verify that fact. From this statement it would appear, that in some of the bivalves, if not in all, the circulation is not without interrup- tion, and that there is a particular one for the special purpose of providing the necessary secretions. With regard to these points I am inclined to think, that the veins of each organ form and supply the secreting glands for itself, in its own immediate vicinity ; for instance, the liver, the bile for the stomach; the ovarium, the mucus for the ova; the byssal gland, the filamentous fluid; the mantle its own pigments; also that thin membrane which is the external duplicature on the shell, springing from its margins, and spreading more or less on all shells, as well as on some of the exposed soft parts of the animal, producing what is termed the pilose skin, epi- dermis, and exterior ligamental covering. There is a difficulty in supposing that all the secretions are elaborated and distilled from a mass of veins collected in a particular cavity, and pro- duce the peculiar secretion for each organ, conveying it thereto by a separate sac or distinct duct. I can scarcely believe that such a concentrated olla podrida can act harmoniously, and produce simultaneously, from a fasciculus of veins deposited in the same reservoir, mucus, pigments, carbonate of lime, &c. "With respect to the digestive organs, the mouth there being no head, eyes, nor tentacula is a large, plain, trans- versely oval aperture, covered by the mantle, and is placed towards the upper part of the anterior range, having on each side of it a pair of palpi, which appear to be both of a tenta- cular and respiratory nature, and perhaps assist the cilia that clothe the branchial laminte to beat and divide the water in 26 BEITISH MARINE TESTACEOUS MOLLUSCA : aid of the extraction of the vital principle. The mouth leads by a short oesophagus into the stomach, concerning which, the elastic stylet, and the tricuspid membrane or stomachal attritor, we refer to the account of the digestive organs of the Pholas dactylus. The food of the bivalves appears to be animalculse and soft Crustacea. From the stomach, which is of suboval or pear- shape form, the intestine plunges obliquely into the lower part of the body, amidst the ovarium, and forms 2-5 or 6 convo- lutions, and at the last turn it ascends to the dorsal range, and, as rectum, discharges at the posterior extremity, either into an anal tube, as in the Pholades, Myce, &c., or without one, fixed externally or floating free, as in the Pectines and Anomice. The liver is usually a large, green, granular viscus, on the dorsal region, almost enveloping the stomach, into which it pours the bile by several ducts or orifices. The reproductive organs scarcely require mention, as they are largely noticed in the anatomy of the Pholas dactylus, above alluded to. We may, however, say, that all the bivalves are strict hermaphrodites without congression. The ovarium varies greatly in form and consistence at different seasons ; in winter it has generally the aspect of homogeneity, but when under the stimulus of the genial months it becomes tumid, flaky or granular, and as fecundation advances the congeries of ova appear in progressive development until the term of gestation is complete, when they are ejected and deposited on various marine receptacles. These animals, though termed self-sufficient, have doubtless mixed up with their ovaria the male influences, which are apparently minute pear-shape bodies, only discoverable in the genial season, containing a glairy fluid, which may be to communicate the vital spark. In some genera, as Anodon, Mytilus, and a few others, the ova are deposited for a time amongst the network or interspaces of the branchial laminae, in which they are further developed, and become testaceous, when they are finally ejected. In reference to the secretions already spoken of elsewhere, we will only observe that the mantle envelopes the entire animal ; its edges are often ciliated, and the posterior end ACEPHALA LAMELLIBEANCHIATA. 27 extended into siplional tubes; the external surface lines the shell, and is the constructor thereof, by the exudations of calcareous matter from its vessels ; the inner surface embraces the body, and is hung and this observation introduces those on the muscular system by some inconsiderable muscles ; but the grand supports of its position, in all bivalves, are the ad- ductor muscles which pass through and suspend the body by being fixed to each valve, and when detached leave cicatrices, termed muscular impressions, which have been applied to assist generic and specific determinations. It is said that in the Anomia, Ostrece, and Pectines, there is only one subcentral muscle : this is a mistake ; as in those genera, as well as in the Mytili and some others, I have found a second muscle, though often of very inconsiderable volume, under the beaks ; w r e may therefore consider the monomyal and dimyal charac- ters as untenable. The mantle in the Anomice, Ostreae, and Pectines is entirely open from the beaks, and destitute of siplional tubes ; in others, as in Lucina, Mytilus, &c., it is more closed, and shows only two sessile orifices ; in the fami- lies of the Veneridee and Mactridte a still further closure is apparent in that membrane, which in them is produced into two short tubes ; in the Tellinidae it forms rather long slender siphons ; and finally, in the Pholades, Lutrarice, Myce, Gas- trochcence, and the Saxicava, it is entirely closed, except a pedal orifice, and is often produced into two long tubes, either soldered on each other or inclosed in a retractile sheath ; the lower siphon is called the branchial, the upper the anal one ; the former conveys water to the branchial cavity and expels it. We do not believe the doctrine that the water enters by one tube and is discharged from another ; we think it is admitted both from the branchial siphon and pedal orifice, and expelled indiscriminately from those apertures. In many genera both, and in others only one of the siphons are pro- Aided with valves at their orifices, to regulate the entry and expulsion of the water, and, with one or more circles of ten- tacular filaments, to capture and transfer the animalcules into the branchial cavity : on this point see our observations on the Pholades. 28 BRITISH MARINE TESTACEOUS MOLLI T SCA: The foot is a very variable organ, implanted usually in the subcentral lower portion of the body ; when at rest, in many families it represents a pedicle, with an elbow doubled up at its side, but in action it becomes instantly straight, pointed, flexible, and extensible more or less in all directions, full of energy and activity. Many of these animals have at the bend at the pedicle a byssal groove, from which tenacious filaments are spun, that enable the animal to fix itself in situations where such action is required, and detach again, which is always effected by the extraction of the byssus from its origin, leaving it fixed at the last locality, and w r hen necessary, spin- ning another with great celerity ; not as a matter of course, but in case circumstances, as currents and rapid tides, require such aid. As to the nervous masses, they are few and scanty, a single ganglion being placed above the mouth, the other posteriorly ; but they are connected with each other by filaments, from Avhich threads ramify to all the muscular supports of the body, particularly those important ones the adductors, the foot, siphonal retractors and minor muscles : the muscular compo- sition of these organs appears in their textures under every imaginable superficial, horizontal, and perpendicular angle. As the shell or hard parts of the bivalves are essential ele- ments of their composition, I am bound to give them some consideration ; I shall however only make a few remarks on the ligament and cartilage, as well as the teeth ; the former is chiefly intended, aided by the teeth, to maintain the valves iu a symmetrical position, when the cartilage is unbent, by the relaxation of the adductor muscles. The cartilage is the great source of elasticity, arising from the impacted mass of fibres of which it is composed, that give its substance almost the appearance of homogeneity. When the animal closes the shell by the retractive action of the adductors, its spring is then bent, and on relaxation the valves are opened to the extent the adductors are relaxed ; but if they are divided by the knife, the elastic power of the cartilage opens them to the fullest extent, at least until they are stopped by the beaks and umbones. Whether the cartilage is termed external or in- ACEPHALA LAMELLIBEAXCHIATA. 29 ternal, or half witliin and half without, its modus operandi in either case is as I have described; and the ligament, as far as its power extends, acts precisely the same. The ligament is always exterior in reference to the cartilage, often covers it, and is fixed to the external margins of the shell, whilst the cartilage rests on the internal marginal surfaces and callosi- ties that act as a fulcrum, which in many species is aided by an apophysis, pit, or excavated internal process. The teeth, with which a large portion of the bivalves are furnished, are strictly of a calcareous nature ; and I am not aware that they have other uses than literally to act as a hinge, and to assist the ligament and cartilage in strengthening the closure of the valves and maintaining their proper position. In some genera where there are no teeth, an accessorial ossicle clasps the two valves as an equivalent; and in those that are entirely mute, the power of the adductor muscles is invariably increased. I have stated, in the preceding paper, that the teeth, ligaments, cartilages, and cicatrices of the muscles, afford, from their variableness and instability, no efficient assistance in forming a continuous natural order; therefore these appendages of the shell will receive no further consideration in any remarks I may make on the natural arrangement of the families of the Acephala ; they may, how- ever, assist in specific distinction, and as accessories and make- weights in balanced investigations. I will now make a few observations on the lacunose doc- trines that have lately been promulgated by the French and Belgian naturalists, which we believe have their origin in M. Cuvier's celebrated Aplysia case, in which it is stated that the vena cava or great branchial vein is perforated so as to permit its contents to mingle with the fluids of the abdominal cavity. M. Cuvier considered this structure so unusual, though he communicated it to his friends, that he hesitated to make it public for many years, until he had by every possible test satisfied himself of this almost unnatural phenomenon, which he declared to be the most extraordinary he had ever met with. I think, if that illustrious naturalist had lived in our days, he would have seen cause to change his opinion., and that 30 BEITISH MAEINE TESTACEOUS MOLLUSCA: the strange appearances he observed were the result of the contraction of the muscular fillets of the vena cava rupturing the extremely thin and almost invisible films of the interspaces of the vein, in consequence of the shock the animal received from sudden death, by spirit, boiling- water, or any other mode of asphyxia. I have already stated, in the observations on the Lamelli- branchiata, that some malacologists are of opinion, that in the Conchifera all the blood conveyed by arteries to the system is not carried back to the branchiae for aeration by a direct vascular apparatus, and that a portion of it is again passed into the system either through the auricle and heart or other- wise, without having undergone the respiratory process of purification. But the moderns have gone far beyond these venous irregularities, and assert that in every molluscum, from the Tunicata to the Cephalopoda, though the blood enters the system by arteries, a part of it reverts to the respiratory centre, by lacuna, cavities, canals, hollows, and fissures, not by veins and walled tubes, which exist in the tissues of the flesh of the animal ; and that the blood, by meanderings, exu- dations, and filterings through these labyrinthine sinuosities in its passage for respiratory aeration, is mixed with the abdo- minal and alimentary cavities and their fluids, from whence they are collected by what are called branchio-cardiac vessels, and transmitted to the heart. With respect to this process I doubt it altogether, and make the same observation on it as on the Aplysia case above, that the excessively fine vascular membranes are at their larger terminations attenuated and often destroyed by contraction and lost by collapse, and become in the animal killed by violence so amalgamated with the tissues as to be invisible, and thus their sites have the appearance of lacuna, &c. I believe this to be the true solution of the apparent absence of venous ducts, and that, though of extreme tenuity, they exist in the live animal. Nature always acts with order and consistency, and it is difficult to suppose she would so far depart from these attri- butes, after having constituted a particular set of vessels to ACEPHALA LAMELLIBRANCHIATA. 31 convey the blood throughout the system, and another visible elaborate apparatus to eliminate the vital element, that she would stop in the midst of her career, and, instead of a set of vessels to convey it back to the branchiae for oxygenation, substitute and allow the stream of vitality to find its way through a mixture of cavernous sinuosities, and percolate amidst the ordures of the visceral contents to the mouths of the branchio-cardiac vessels, to pass it to the respiratory me- chanism to repair the usual exhaustions and adscititious impu- rities of its passage. Neither of these opposite views can be verified in the living- animal, and the examination of the dead one is equally unsa- tisfactory, because uncovered sinuous canals may appear to exist in the tissues ; but who can say that the excessively thin walls may not have vanished by contraction attendant on the peculiar mode of death, leaving only the sinuosities of their sites ? The above remarks are confined to the circulation of the blood. I fully admit that in many of the Mollusca, aquiferous canals and pores exist in the tissues of the foot and its pedicle, and other organs for the admission of water to assist in pro- moting the tension of those organs in aid of locomotion ; but I do not believe that the water enters the visceral regions except by the mouth, unless in consequence of a rupture of the parti- tion-membrane between the cavities of the foot and the abdo- men ; it has been stated that the Lucinas are instances of the water passing through the foot into that cavity. For these reasons we repudiate, as contrary to nature and all analogy, the doctrine of even a qualified lacunose system for the blood circulation ; that is, of its being sent by arteries to all parts of the organism, and returned partly by walled vessels, and partly by sinuous canals worked out of the paren- chyme. And in the tribes of inferior organization to the Mollusca, we consider, however imperfect the mechanism of the susten- tation. and circulation may be, that both these functions are distinct, and in no case confounded; we believe that nine- tenths of the matter that has been advanced by authors on 32 BRITISH MARINE TESTACEOUS MOLLUSCA: these points are little better than hypotheses, and rest 011 unsound demonstrations. It is well known that the mind, deeply intent 011 the examination of the very minute objects of natural history, when jaded and exhausted by the pressure of high microscopical powers, often deceives itself, and from preconceived impressions, idealizes and fancies it sees objects that have only an imaginative existence, and strongly distorts real ones through optical illusion. We admit that in the lower Invertebrata there is no mecha- nism for sustentation, circulation, and respiration, of the com- plex and advanced character of the Mollusca, as heart, auricles, arteries, and veins; but though these inferior grades do not present the strict homologues of these organs, we think that there are in them analogical substitutes, which rescue the simplest of these beings from the confusion and unnatural admixture of organs and functions that have not the commu- nity which authors have ascribed to them. Though a heart and circulatory vascular structure cannot O / be demonstrated in the minuter, and even in some of the largest of the Radiata, we nevertheless believe that they exist, as well as a distinct visceral cavity and canaliferous walled recipient for the aliments, and that the two mechanisms are not otherwise connected, except by the former receiving from the laboratories of the latter the influences and elements to invest the blood with the power of sustaining life, after it has received the impress and interchange of the gases with those of the exterior or interior fluid aerating elements bv endos- O if mose or exosmose, and thus establish the vital principle. And further, we are of opinion that muscles and nerves are present in the lowest of these organisms to excite motion and sensation to an extent commensurate with their wants. On this head we cannot help quoting a passage of ours in the ' Annals of Natural History/ vol. v. p. 161, N.S., in a paper on the Foraminifera : " On the question of the nervous and muscular influences, which Lamarck only admits, as independent of sensation and interior sentiment, in his apathetic animals, amongst Avhich are the Polypi, I must be allowed to make a few observations, ACEPHALA LAMELLIBRANCHIATA. 33 to explain my reasons for not concurring in the views of that great naturalist. Lamarck contends that sensation, or interior sentiment, does not exist in the lower animals, and that in them all movements arise from irritabilities excited by exter- nal impressions : I demur to this doctrine, and firmly believe that no created being can exist and exhibit evidences of vitality, by motion, without having implanted in it a certain degree of sensation or interior sentiment, by the influence of which the nervous and muscular powers are put in action. I grant that external causes may produce motions and contrac- tions, not I think by exciting an irritability independent of sensation, as Lamarck terms it, but by the agents and after the manner I have just stated. " It will be admitted that the sensations in the lower animals, which are the origin of the nervous and muscular influences, are of the most subdued cpialities ; and though the points of departure of the nerves, and the muscular supports dependent on them, may not be discernible by the most powerful instru- ments, still I believe that they exist, and produce those move- ments which are observed in the monad as well as in man. In the superior and larger animals, we can perceive the causes of these influences and admit their existence, because they are apparent ; and why not in the smallest, though they escape our vision ? In the nearest fixed stars we can observe their proper motions, but in those which are plunged in the deeper regions of the sphere, these motions, though we may presume that they undoubtedly exist, are inappreciable. Why may we not apply a similar reasoning to the doctrine of the sensations or interior sentiment, and the resulting nervous and muscular influences, being implanted in the lowest as well as the highly organized animals, according to their several structures, and not consign vast classes to exist without sensation ? It ap- pears to me that the lines of separation between apathy, sensa- tion, interior sentiment, and intelligence, as laid down by Lamarck, are erroneous and arbitrary. I believe that apathy in its strict sense, as applied to animals, does not exist ; and I repeat, that the most inferior created animal being is not without that portion of sensation or interior sentiment, and D S4 BRITISH MARINE TESTACEOUS MOLLUSCA: its concomitant nervous and muscular influence, that produces the motions which are the tests of vitality. I may state that Lamarck does not admit the distinction of intelligence and instinct ; he very justly considers the different degrees of what is called instinct, in animals, as only subdued intelligences consequent on their imperfect organs, when compared with the highest standard man." The contents of the visceral cavities or walled ducts, whether they consist of solid food or chyliferous fluid, have precisely the same function as in the higher animals, that of susten- tation ; and whatever may be the nature of the blood fluids which fill the vascular apparatus of every living being, and all have one, we think they ought to be termed the true blood, as it always flows in parietal contractile tubes, arteries, or veins, and never in excavations called lacuna, burrowed in the parenchynae of the animal. These lacunae do not apply to visceral matters ; they are simply aquiferous canals to give tone to the various muscular organs of the Invertebrata, and not for the circulation of blood. When we say that a vascular circulating and respiratory system exists in the monad as well as in man, we admit that these organs are often simplified to the extent of the requirements of the various tribes. We do not contend that the elaborate structure of the higher inverte- brates obtains in the radiate organisms; but we think that if there be not a heart receiving blood by auricles, and con- veying it by arteries and veins through a general circulatory and respiratory apparatus, there are in the simplest beings equivalent conditions, and that the typical heart of systole and diastole agency is often represented in the vascular me- chanism by receiving from muscular contractibility and relaxa- tion a power which gives a sufficient impulse to the blood to secure its enrichment and aeration. And further, with respect to the circulatory apparatus of these inferior organisms, though its tubes and cavities may not have the gradual decrease and increase of the arteries and veins as in the higher animals, nor consist of an afferent and efferent set of vessels, we consider that the substitutes of these organs are sufficiently supported by analogy, if the blood is TEKEBRATULA. transmitted for the nourishment of the body through tubes and variously-shaped walled canals or cavities, though they be neither typical arteries or veins ; we go further, and believe that in many of these beings a blood circulation may be as effective through a single walled canal as by a more complex arrangement, and thus receive the necessary aeration, which in most of the lower Invertebrata is probably cutaneous and effected by endosmose, and that in those animals in which the ambient element can only be admitted into visceral cavities, it is oxygenated by exosmose. ACEPHALA PALLIOBRANCHIATA. Having already mentioned most of the incidents of this family, I have only to add, that it consists of three genera, Hypothyris, Terebratula, and Argiope. None of the animals or the shells have occurred on the Devon coasts, except the Argiope cistellula, and that only in a dried state. HYPOTHYRIS, Phillips. H. PSITTACEA, Chemnitz. H. psittacea, Brit. Moll. ii. p. 346, pi. 57. f. 1, 2, 3. We can only refer to the first vol. p. 150, of the ' Zoological Transactions/ for Professor Owen's account of this animal. The shells of this genus are never punctated. A very doubt- ful British species. TEREBRATULA, Bruguiere. T. CAPUT SERPENTIS, LimiEeus. T. caput serpentis, Brit. Moll. ii. p. 353, pi. 56. f. 1, 2, 3, 4. The valves of this genus are always pimctated, and particu- larly so in this species ; it is taken plentifully on the Scotch 36 TEREBEATULID^;. coasts. We refer to the second vol. p. 355, of the ' British Mollusca ' for a description of this animal. T. CRANIUM, Miiller. T. cranium, Brit. Moll. ii. p. 357, pi- 57- f. 11 ; and iv. p. 257. This species is said to have occurred in Zetland. The animal has not been observed. ARGIOPE, Deslongchamps. A. CISTELLULA, Seaiies Wood. A. cistellula, Brit. Moll. ii. p. 361, pi. 57. f. 9, and iv. p. 257- We have taken this species in the coralline zone, at Ex- mouth, with the animal in the shell, but perfectly dry ; and all that is known of it is, that it has spiral arms supported by an apophysary process. The present shell is quite fresh ; it is of subquadrate form, pale brown colour, much more compressed than the Shetland specimens, and has the mesial groove more distinctly deve- loped; still it is only a variety of the Megathyris cistellula, which M. Philippi states to be subject to much variation of out- line. Axis et diameter y 1 uncise. I have again recently taken from the coral zone of the South Devon coast, at Exmouth, in thirteen fathoms water, the M. cistellula, now Argiope cistel- lula of the ' British Mollusca/ the Terebratula seminulum? Philippi, which I believe has not been found so far south in the United Kingdom, except fide Turtoni, in Torbay ; I am sure that Professor Forbes and Mr. Hanley will feel pleasure in the corroboration of the correctness, in this instance, of Dr. Turton's habitat : see the note in the ' British Mollusca/ vol. ii. p. 362. I have had on several occasions personal inter- course with Dr. Turton, and became the original purchaser of his collection of British shells, which, during my temporary secession from rnalacological pursuits, passed out of my pos- session ; Dr. Turton also did me the honour of the dedication of his Manual of the Land and Freshwater Mollusca. Under CEANIA. 37 these circumstances, I consider it to be my duty, to say, in respect to the note referred to, that I am confident my old friend never intentionally led us into error ; nor do Professor Forbes and Mr. Hanley state otherwise. The fact is, that Dr. Turton was a man of great simplicity, and so far from age giving an increase of caution, it appears, with him, to have had a contrary effect ; if it were necessary, I could relate several curious and laughable stories of his being duped by the frauds of crafty shell- dealers. Whilst I admit that Dr. Turton lent too credulous an ear to the impositions of unscrupulous com- municators, which has impaired our dependence on the habi- tats of various doubtful testacea recorded in his ' Conchologi- cal Dictionary/ I trust I have cleared the memory of my friend, to whom British conchology is much indebted for his care and nurture, from every suspicion of gross and indesinent error : we must not forget that Dr. Turton and the excellent Montagu fanned the flame of this branch of natural history when almost extinct, and its supporters were few and far between. CUANIAD.E. This family has one genus and one recent species. CRANIA, Retz. C. ANOMALA, Miiller. C. anomala, Brit. Moll. ii. p. 366, pi. 56. f. 7, 8, and pi. U. f. 2 (as Norvegica). Animal with pale pink, fringed, spiral arms. The ovarium is red-brown, and deposited partially on one of the lobes of the mantle. It is taken plentifully in Scotland. It is to be hoped that some qualified northern or wayfaring naturalist will fur- nish science with a more extended account of it, and of the Hypothyris caput serpentis, as I apprehend it will be long- before an additional recent species will occur. 38 ANOMIAD^E. ACEPHALA LAMELLIBRANCHIATA. ANOMIAD^E. The ouly genus of this family, Anemia, is one of the Ostra- cece of Lamarck's monomyal order, which cannot be main- tained in its integrity; zoologists have long removed the MytilidfB from it to the Dimyce. It will be as well at once to state, that all the monomyal animals of that eminent naturalist are really Dimyae. It will probably create some surprise when we say, that the only true Monomycs are the Pholades and Teredines, as, we think, we have satisfactorily demonstrated in their respective anatomies. All other bivalve genera have two adductors; the anterior one in Anomia, Pecten, and Ostrea is of so small a volume, as almost to have escaped notice; and the great subcentral muscle in those genera appears* of a size as if the two ordinary dimyal ones were amalgamated ; still the anterior adductor exists, and if carefully searched for will be found under the beaks, pointed out either by a single minute cicatrix, or by a little group of five or six closely united, very small, muscular scars ; this dis- position of the cicatrices varies in all the genera, so does the main subcentral mass, as to shape and size. Careful dissec- tions of the animals will show the muscular filaments adhering to the circumscribed area under the beaks; but in oyster- shells that have been exposed to the action of the sun and air, and vicissitudes of weather, the minute anterior adductor is perfectly visible. In the three genera we have mentioned, these muscles are of small size ; thev, however, in the next t/ * family, the Mytilidce, though still small, have become more developed, and in the following one of the Arcadce they have completely acquired the typical size and position, which is maintained in all the remaining families, until they reach the Pholadidce, when they merge into a single medial adductor, both in the Pholades and Teredines. ANOMIAD^E. 39 Lamarck has made Pecten and Lima the types of the Pecti- nidce, and Ostrea that of the Ostreadce ; so far we concur ; but we must remove Anomia from the Ostreada, with which, though it has the relations of the great subcentral muscle, and absence of tubes, still there are closer ones, of a different character, with the Palliobranchiata and the Pectinida. Though the characters of the great subcentral or posterior adductor muscle, the rudimentary, or no foot, and absence of siphons, are very decided ones, and common to this particular order or race, still it is not necessary that Anomia, Pecten, and Ostrea shoidd on those accounts form a single family, any more than the Veneridae, Mactridce, and Cardiadce, because they have distinct tubes, foot, and are strict Dimyae ; therefore these reasons, and those under each particular head, have determined us to constitute Anomia, Pecten, and Ostrea as distinct families. Anomia then, with its single species, constitutes the family of the Anomiadce, which we fix, according to our method, the first of the Lamcllibranchiata, as it forms the decided point of passage from the Palliobranchiata, by its constant state of fixture, by a prolongation of the adductor muscle, through a perforation of the valve, to marine substances, either by a ligamentous or testaceous point of adherence; it also shows a similarity in the disposition of the ovarium on the mantle, and posi- tion of the animal in the shell. It will be observed that in this statement there is not a single point of community between Anomia and the Ostreadce. Though Anomia, by the small byssiferous foot, and the very singular doubled-up struc- ture of the branchial laminse, shows a very intimate connection with the Pectinida ; nevertheless, from its constant fixity, the perforated valve, ligamentous attachment, the texture of the shell, its proteiform shape, and the hinge, it cannot, without violence to established distinctions, be allocated with that group. I think I have adduced sufficient reasons to support the severance of Anomia from the Pectinida and Ostreadce ; and I consider that there are equally good reasons for the separation of Pecten and Ostrea. 40 ANOMIA, Linnaeus. A. EPHIPPIUM, Linnaeus. A. ephippium, Brit. Moll. ii. p. 325, pi. 55. f. 2, 3, 5, 7; and animal, pi. T. f. 2. Anomia ephippium, A. electrica, A. cepa, A. squamula, A. aculeata, A. striolata, A. punctata, A. cylindrica, A. tubularis, A.striata, A.fornicata, A. coronata, A. patelliformis, A. undulata, Aucto- rum. A. aculeata, Brit. Moll. ii. p. 332, pi. 55. f. 4. A, patelliformis, Brit. Moll. ii. p. 334, pi. 56. f. 5, 6. A. striata, Brit. Moll. ii. p. 336, pi. 55. f. 1, 6, and pi. 53. f. 6. Animal subdepressed, with its periphery suborbicular ; mantle circular, the upper portion, or the one forming the convex valve, of very thin and pellucid texture, except at the anterior margin, which is thick ; and the under part, or that lying on the flat valve, is also thin, hut has the appearance of being fleshy from having the ovarium soldered to it ; both are clothed with a double fringe, which diminishes in breadth as it approaches the beaks, and passes round the aperture of the operculum, there throwing out cilia, and then is fixed under them. The outer circle of fringe consists of long, yellowish white, sharp-pointed tentacular filaments, which are, when undisturbed, continually protruded beyond the shell, and on the inner circle there are long and short cilia of the same colour distributed irregularly ; but the colours of the fringes and their marginal areas vary from a mixed blotchy red to yellow or purplish brown. No ocelli can be detected. There are a pair of circular branchiae varying from pale red to dark brown on each side of the body, with fine longitudinal and transverse vessels, presenting the appearance of a delicate net- work ; the plates of each pair have a part of their outer sur- faces double, and form circular open pouches, the upper part of which is well defined by the branchial vein : thus each single plate presents the aspect of two, and the two pair of branchiae appear composed of eight plates; but the doable parts can easily be placed in length, by the insertion of a camePs-hair brush in the hollows, and again be returned to the double ANOMIA. 41 position. This curious configuration of the branchiae is that of the Pectines, but not of the Ostreae. At the anterior side, which is easily known by being oppo- site the conspicuous anal tube or if the shell is placed on its front edge, with the perforated valve to the right hand of the observer, it will be farthest from him is situate the oval margined mouth with its large aperture, which is very high towards the dorsal range, and has around it two plain linear membranes that are continuations of the branchiae, which at this point have become slender. These laminse expand at each side the mouth into two pair of long delicate labia, fixed by the entire length of the longest sides, folding on each other ; they are finely striated on both surfaces ; the colour is light to dark brown. The foot is almost reduced to nothing ; it is fixed to the body under the mouth, and is a small, yellow, obtuse, subcyliudrical, pendulous, deeply-grooved organ, capable of spinning a byssus, which we have seen, and may serve to fix the animal in conjunction with the operculum. It is strange that nature should have furnished this animal with a foot and byssal groove of so small a size as apparently to be of little use, unless we suppose it to have the power of freeing itself from the bodies to which it is attached; and this idea is by no means without the verge of possibility. It is known that the Arcae, Pectunculi, and other byssal bivalves, can detach themselves from their fixed position by abandon- ing the byssus. May not the Anomice dissever the end of the adductor muscle from the calcareous operculum? This in- ference arises from the presence of a byssal foot, which would then have a pro tempore use, whilst the animal in a change of locality is again fixing itself. These ideas are fortified by the statement of our dredger, who affirms that he is constantly hauling up pieces of rock studded only with opercula : this fact is certainly no proof that the animals detached them- selves, but it is a link in a chain which has a certain value. Nevertheless we are inclined to think the genus a fixed one for life. The ovarium is an extensive, inflated, sinuated lobe, origi- nating on each side the liver, coasting the body, and glued to 42 ANOMIAD^H. the lower half of the mantle; this organ has been mistaken for a large foot, but its soft, pulpy, granular composition shows that it is the organ of reproduction, and the milky humours arising from various pyriform membranes, in the genial season, which are only then discoverable, are probably the male organs of fecundation. The colour of the ovarium, as well as of the body in general, is very various ; sometimes they are of a pure vermilion, and from that, passing into every hue of that colour, as well as into all the shades of yellow and pale red-brown. I have seen all these colours in groups of the Anomia ephippium, on the same Pecten ; whilst in others all the objects on the same shell have maintained a uniformity of colour. The same discrepancies prevail in A. aculeata, A. striolata, A. cylindrica, and A. squamula. These differ- ences, combined with the various markings, shapes, spines, ribs, and strise, generally resulting from similar markings on the substances on which the shells are fixed, have doubtless been the cause of the multiplication of the species, as in all the varieties enumerated, not excepting the A. striata, which is the A. patelliformis of the ' British Mollusca/ the organs, as far as they have been examined, have not presented marked differences, except in colour. The liver is always of the va- rious shades of green, placed under the beaks, at the centre of the dorsal range ; the passage from the mouth to the stomach is a short gullet, and these organs are situate under, and partly surrounded by the liver ; from it the intestine descends to the centre of the body, where it makes some turns, then ascends through it and the ovarium to the dorsal range, and issuing therefrom, passes behind the body and the posterior siiiuation of the ovary, slightly attached to their membranes, and debouches at some distance from the base of the posterior ventral range, as an uncovered rectum. In most bivalves the muscular impressions are supposed to assist specific distinction, but this idea is fallacious with re- spect to the Anomia. In this genus the circumscribed line in the convex valve contains the impressions of the muscular mass, which divides itself into tliree cicatrices, one by itself and the others on the right and left of it ; these impressions ANOMIA. '!'* are never exactly of the same size, nor do they preserve their relative positions in any of the varieties, in consequence of the animal dividing the muscular mass into three fasciculi of fibres, varying in quantity, thus altering the shape and relative distance of one portion from the other ; therefore these impressions are of little distinctive value. Finally, as regards the animal, it may be observed, that in this singular unsymmetrical genus, even its organs display, like the shell, varieties of form; this arises from the entire animal being deposited in the convex valve ; it only rests on the flat one, and the organs, in consequence, vary with the ever-varying figure of the upper valve. I will now make some remarks on the various markings and aspects of the shells of the so-called British species, of which I have examined above a thousand. And as regards their general shape, they vary from all grades of subcircularity to every subtriangular form. I have seen on the same Pecten, on the shells of which genus the Anomite are oftener fixed than on any other, two individuals of the typical dirty-white A. ephippium, the one displaying its strictly squamous cha- racter, and marked not only with ribs, but the vaulted and arched spines of the Pecten ; the other, in contact, without a rib or spine, and only showing the regular squamse of increase. I have also seen the A. ephippium with half the transverse portion of the shell of a perfectly squamous character, and the basal half ribbed and spiny, and vice versa. The same inci- dents are seen in the rosy purplish A. cepa and bright yellow A. electrica of British authors, which are mere deviations of colour from the type. As for A. striata, otherwise the A. undulata of some authors, which is certainly the most aberrant form of the A. ephippium, the distinctness of which has been insisted on from the iri- descent green colour of the inside of its valves, the radiating muscular impressions and the intense vermilion of the ani- mal, I have to observe that in young specimens, of one and a half inch diameter, having the anastomosing radiating strise found on the smooth insides of the Pecten maximus, I have noticed these characters to be by no means constant, having 44 ANOMIAD.E. frequently taken delicate, pale, dirty white-brown shells with similar markings, without an appearance of the green insides, and instead of the vermilion animal, they presented a pale yellow aspect; in addition, I have taken from rocks hauled up from the coralline zone, A. ephippium of 3f inches dia- meter, with and without anastomosing striae, and the insides varying from green to light brown and white; and I have little doubt that all the variations I have mentioned are those of the type, A . ephippium, which under no circumstances loses its characteristic sq^^amous character. With regard to the young or dwarf A. ephippium, A. squa- mula, A. aculeata, and A. striolata, grouped and crowded on the Pectines, I believe they are mere dwarf varieties of the type ; these often adopt the markings of the substances on which they are fixed, and as often show a complete disregard thereto. I have seen shells combining all the supposed di- stinctive marks in one individual, in which the decided, smooth, glossy A. squamula has commenced the umbonal part of the structure, gradually in respect of the middle portion, gliding into the squamous A. ephippium, and dividing the basal part right and left, the one into the asperities of the A. aculeata, the other into the delicate smooth striulae of the variety^. striolata. Nothing is more common than to see shells half A. squamula and half A. ephippium, and other admixtures of the characters of two or three supposed species. The last- named four varieties are also found at the roots of Algae, but both in colour and the union on the same shell of each other's distinctive marks, they present the same incongruities and discrepancies as their brethren on the Pectines. The A. cylindrica or A. cymbiformis, a variety of the A. ephippium, takes its hollowed appearance from embracing the roots of the Fuci; the A. tubularis, another variety of the type, has the margin of the aperture elongated, to suit its condition to some irregularity of the substance on which it is placed. The A. punctata is also a young A. ephippium with papillae-like eminences on the convex valve, and corresponding depressions on the flat one, arising from similar markings on the substances on which thev are fixed. I do not know the PECTINID.E. 45 A. fornicata and A, coronata recorded by Mr. Bean, but I learn from the ' British Mollusca' that they fall into the same category with those I have named. I have now noticed all the varieties of A. ephippium termed by authors species, and there is certainly no sculpture on them of such a decided character as to denote specific distinc- tion; therefore all the markings, shapes and colours of this Protean genus being inadequate for the foundation of species, we must have recourse to our sheet-anchor the malacology of the animal to assist our determinations ; and after the examination of a great number of individuals, of nearly all the recorded species, we have come to the conclusion that they are varieties of the only British one of this genus, the A. ephippium, which, by the identity of its organs with the pseudo-species, puts a veto on a longer continuance of the dismemberment of its unity, by allowing forms based on mere varietal distinction to march pari passu with it, and which have no solid grounds for aspiring to higher honours. PECTINID.E. The British Pectinidce comprise only the genus Pecten, which is a part of Lamarck's monomyal order. The genus Lima, usually associated with Pecten, is merged in it as a section. Our reasons for distributing the Anomite, Pectines, and Ostrete in three families, are given in our remarks on the Anomiadae, wherein the essential points of the differences of the organs and habitudes of their animals are shown ; we may add, that the texture of the shells of this group has lost the leafy imbricated character and become firmer, solid, and of a more porcellanous nature ; their form is infinitely more symmetrical than in either Anomia or Ostrea. A careful examination of the descriptive notes of the animals of the Pectinidas will show that they are not of the same family as either of the other groups. 46 PECTLNID.E. PECTEN, Bruguiere. * Shell firm, solid, of a porcellanous texture. P. OPERCULARIS, Linnseus. P. opercularis, Brit. Moll. ii. p. 299, pi. 50. f. 3, pi. 51. f. 5, 6, and pi. 53. f. 7- Animal suborbicular, thick, lentiform; this shape results from the support given to the organs by the powerful central circular adductor muscles ; the colours are very variable, Avhite, pink, fawn, orange and brown; the body, with the amalga- mated ovarium, is a compound of flake-white meandering lines, spots and blotches, and its conical termination is of the palest vermilion to the intenser hues of that colour ; it de- scends from the dorsal to the ventral range, on the anterior side of the great subcentral muscle. The mantle is thin, except at the fleshy margins, and open throughout, with the exception of a short dorsal area; there is not a trace of siphons; it would be too large for the shell if it were not doubled on itself and fixed a little within the duplicature to the shell by very slender muscular pallial threads. At the folding a cord-like margin springs, but the true mantellar margin floats loose, and is considerably within this line ; both are furnished with 23 rows of irregularly deposited, conical, white, pointed cirrhi of three different lengths ; those of the inner circle are tinged with brown ; the outer or fixed range has the longest filaments, and in addition 35-40 subglobosc ocelli that have pearl-coloured pupils within black circles; these vary in size, and extend at equidistances throughout the peripherial range to the auricles. The foot springs from the body just beloAV the palpi ; it is yellowish white, subcylindrical, of small volume, deeply cloven or furrowed, and scoop-shape at the termination ; it appears to have no locomotive use, and only to be the vehicle for pro- ducing a byssus for occasional fixation, especially of the young animal. I have seen most of the species thus fixed. There arc a pair of subcircular branchiae on each side, vary- ing in different individuals to all shades of the colours above PECTEN. 47 named, deep, and of similar depth, very thin and delicately reticulated ; the outer surfaces of each pair, as in Anomia, with which Pecten has alliances, are doubled on each other, and form circular pouches when in natural position ; but these duplicatures can be put straight and again returned. In connection with them, on each side, are a pair of broad short palpi, rounded at their extremities, fixed laterally to the body and to each other, so that they fold as the leaves of a book ; they are smooth without and well pectinated within, of a yellow-brown or pale orange colour ; each pair is united with the other around the mouth by two cordons of 5-6 short, dull orange, fimbriated cirrhi; the mouth is between them, and passes by a short oesophagus into the stomach, which is im- mersed in the extremely dark granular liver, and contains the usual stylet and attritor or tricuspid membrane ; the intestine plunges to the bottom of the body, and again ascends to the dorsal line passing around, embraced by the heart and becoming fixed to the posterior side of the great muscle, debouching at nearly the ventral level. The ovarium is mixed up with the body ; its surface is studded with ova, and the vermilion termination contains a milky fluid which may be the fecun- dating influence; it is only in the genial season that this appearance is seen. We have no faith in the doctrine of the bisexuality of the Acephala ; in many it is impossible for a contact to ensue. The locomotion is effected by the animal with the posterior end in front suddenly opening and closing the valves, which action, as we have repeatedly witnessed, produces a motion as rapid as that of a Lobster or a Sepia. This species being more universally distributed than any other, may be considered as the type of the British Pectines, in which the organs present almost an identity of form. The specific differences consist chiefly in the colours, and in the arrangement and size of the cirrhi of the margins of the mantle, together with a general but unmistakeable aspect in each species, which affords the practised eye sufficient di- stinctive characters ; but if the younger student is at a loss to appreciate the animal specialties, he will obtain much aid from 48 the conchological indices, which afford valuable corroborative assistance. At Exmouth this species is taken in the coralline zone in great abundance ; so much so, that they might be, perhaps, preserved in jars, if their delicacy did not prevent sufficient firmness, and would prove a more delicious morsel than the pickled oysters of the Italian warehouse. P. VARIUS, Linnseus. P. varius, Brit. Moll. ii. p. 273, pi. 50. f. 1. The general structure and composition of this animal is so similar to that of the type, P. opercularis, that it will only be necessary to note the specialty variations. In this species, the reflected or inner free margin is, as to colour, marked with pale red or brown irregular blotches, with the edge fringed with a single row of thin, white, blunt filaments, which, though short, vary in length ; the outer or fixed margin has at the innermost part, at equal distances, a row of long, conical, light yellow cirrhi ; to these succeed 30-35 ocelli, which have more black and a less pearly appearance in them than in the tvpe ; and the outermost paraphernalia of this margin consists of two irregular rows of extremely fine, snow-white filaments of three lengths. The branchiae are in all respects similar to the type, except in being of the palest drab ; the body and ovarium, which is amalgamated with it, is of a pale yellow cream-colour, mottled with thick-set flakes, which have the aspect of ova ; we are not sure if the vermilion colour ever appears in this species ; all its organs are of a much more deli- cate, elegant and refined aspect than in any of its congeners of similar bulk. The intestine terminates by a short, white, slightly grooved rectum, spatulate at the end. The labia are pale fawn, and the two connecting foliated rows of fringe of light drab. The ovarium, or that part of the body consti- tuting this organ, is at this season, August, full of ova, and an opake red milky fluid, as in the type. We here repeat, that we do not believe in the bisexuality of the Acephala, by which term is meant that each individual is either male or female. PECTEN. 40 The foot emits a powerful coarse byssus, which cannot be detached without laceration of the body, but the strands are easily separated from the substances on which they are fixed ; this is contrary to the usual plan of the Bivalves, which, when a change of locality takes place, is effected by drawing the byssus from that part of the foot-groove close to the body, and leaving it moored to the substance on which it was fixed : this operation we have witnessed even in confinement. This species is given as an example of the variation of specialties ; all the others afford nearly as decided ones. I trust that some northern observers will compare the P. tigrinus, P. striatus and P. furtivus, all of which we believe are identical, and communicate the result: if they are distinct, malacologists will have no difficulty in seizing the distinctive characters. Speaking conchologically, we should say that the three so-called species are only variations of the old P. obso- letus of authors, now styled P. tigrinus. This species is either free, or adheres by the byssus to marine substances, but is not imbedded in them by the under valve, as in the P. pusio. P. PUSIO, Pennant. P. pusio, Brit. Moll. ii. p. 278, pi. 50. f. 4, 5, and pi. 51. f. 7- P. distortus, Montagu. P. sinuosus, Tin-ton et Auct. The body and ovary throughout are either intense vermi- lion, or of a uniform pale yellow-white, and not half white and half vermilion, as in P. opercularis ; at least in P. pusio we have never observed this to be the case. The branchiae are dull red-brown, and the palpi pale brown ; there are two connecting rows of pale red cirrhous fringe around the mouth. The back or free margin of the reflected mantle has two to three rows of irregular, short, yellow- white, blunt filaments. The ocelli are larger, fewer, and more distant than in the type. The fixed or anterior marginal circle has a row of large, long, conical, pointed, yellow filaments, and in front of it two to three irregular rows of shorter cirrhi of different E .i() PECTINID.E. lengths ; the mantellar marginal areas are a blotchy mixture of fawn, yellow, pale red-brown, and lead colours. This species comes much closer to the type than P. varius. From the great variableness of the colours in the same species, and the general similitude in the structure of the organs, it is sometimes difficult to seize the specific distinctions of closely allied animals ; in such case we must call in aid the figure and markings of the shell, which being dependent on the dispo- sition of the secreting glands of the mantle, cannot well be malacologically appreciated. This case strongly supports the views laid down in the paper on the Littorince, in the May ' Annals of Natural History/ 1850, wherein we strenuously contend for the examination of both the animal and the shell to ensure a true distinction of species, as when the soft parts do not afford sufficient characters, the shell may assist in re- ' */ solving the difficulty. This species is usually imbedded in masses of Flustra and old bivalves by the under valve. P. SIMILIS, Laskey. P. similis, Brit. Moll. ii. p. 293, pi. 52. f. 6, and (animal) pi. S. f. 1. Shell suborbicular, depressed, but equally convex on both surfaces ; the auricles are not greatly dissimilar, the posterior, however, is the smallest, their terminations are sometimes rounded and sometimes obliquely truncate. There is very little sculpture on either valve beyond the fine subcircular strise of increase, and rarely there are faint traces of ribs, but the markings on both surfaces are very variable in figure and colour ; they exhibit every combination of blotches of all hues, and sometimes a series of markings simulating radiating ribs so closely as to be difficult of detection ; but these appearances, under proper optical powers and light, will be found to be in the test, with the surface quite smooth. We have taken such specimens alive in the coral zone at Exmouth, from one of which are derived the notes on the animal. Diameter less than a quarter of an inch. Animal of the same form as the shell, and as variable in its PECTEN. 51 colours. The mantle is pale yellow, furnished, as is usual in the Pectens, with a fixed and free margin ; the latter is clothed with about twenty long, white, triangular, frosted cirrhi with shorter intermediates ; from the minuteness and delicacy of the animal the filaments of the fixed margin were not detected ; the free margin between the cirrhi is marked with blotches of all sizes, of the colours yellow, bistre, rufous, and black ; the ocelli are 1620 ashy circles, having in their centre a minute ring or pupil of a smoke colour. The branchiae vary from light yellow to dark lead colour, but the very fine darker lines are generally relieved by intermediate lighter ones ; they, like their congeners, have the lower part of the area of each gill- plate reflexed on the upper, forming subcircular pouches. The small foot, producing a byssus, is situate very high, almost immediately under the anterior dorsal margin, and varies from Avhite to vermilion. These variations in colour of the shell and organs of the same species are one of the characteristics of the tribe. The foot appears to have little power of loco- motion, but by spinning a byssus it produces a mooring appa- ratus. The animal, by flapping the valves, effects a rapid progression. This very distinct species has been considered by some as the young of Pecten maximus, but the convexity of both valves negatives this idea. At all ages the P. maximus has the upper valve flat, with a concave area at the beak. P. MAXIMUS, Linnseus. P. maximus, Brit. Moll. ii. p. 296, pi. 49. In this beautiful and well-marked species, both by the shell and the animal, the inner margin of the mantle has only a simple row of very short, white cirrhi; the fixed anterior margin has three ranks of filaments of different lengths not deposited in perfect serial order, the largest and longest are pointed, and on retraction become curled in a spiral form ; all the cirrhi on the upper or flat valve are marked in the centre, from base to point, with a pale red-brown line, the under surfaces being white; the cirrhi of the convex valve E 2 52 are pure white on both surfaces. The membranous marginal areas of the mantle are elegantly arranged in meandering lines of pale red, brown and yellow, forming various-shaped lozenges. "When the valves are opened, and the mottled surfaces of the double margins of each valve are in conjunc- tion, and the various circles of filaments and cirrhi fully ex- serted in a shallow basin of sea- water, it is scarcely possible to conceive a more beautiful and interesting appearance. There are two rows of sea-green ocelli relieved at one part of the circle by a black point, with the pearly pupils deeply sunk in their hollows; there is usually a large eye under each rib of the shell ; the others are much smaller, deposited in a row under them; they all amount to about thirty to thirty-five. The branchise are small for so large a species; there are a pair of palpi on each side, pale drab or brown, laterally attached, folding on each other, subquadrangular, composed of twelve to fifteen strands pectinated on both sur- faces, but more intensely on the inner ; the buccal fringes are two rows of very bright red, well-foliated and branched fillets, which connect the palpi ; the mouth is in the centre of them. The body, and the ovariuin amalgamated with it, are of very small volume and usually white. The foot is snow-white, short, grooved, with a spatulate extremity. The liver is quite dorsal, black-brown, or an intense dark green. The brown suboval secreting glands on each side are as conspicuous in Pecten as in Ostrea. We may observe, that in all the Pectines the mass of the organs is small, and appears scarcely commensurate with the area of the shell ; perhaps the deficiency is made up by the mantellar extensible margins and cirrhi, which coast the pe- riphery, being only interrupted by the very short ligamental area, from which point, on each side, they gradually increase in width and size to the centre of the aperture. The animal can effect a rapid progression by flapping together the valves, with the ventral margins in front and the flat valve upper- most. This elegant and edible species, the Prince of the British Pectines, is frequently taken in the coralline zone at Exmouth. PECTEN. 53 Some malacologists think that the P. niveus of the Caledonian shores is a variety of P. varius we believe from the shell it is distinct, but the animal must determine ; it has not occurred on our southern coasts. The P. tigrinus, the P. obsoletus of authors, is frequently taken alive in Exmouth Bay ; but it is a variety, though ribbed at the margin, of a smoother mould than the Scotch specimens, which from their variableness have been manufactured into three or four species, as before observed. The P. danicus is Scotch, and the P. islandicus probably spurious. ** Shell thin and of vitreous texture, varying from a perfectly symmetrical to an oblique outline. P. FRAGILIS, Montagu et nobis. Lima Loscombii, Sowerby. , Brit. Moll. ii. p. 265, pi. 53. f. 1, 2, 3. We have yet to learn why this animal has received the spe- cific title of " Loscombii :" surely the far prior and more ap- propriate appellation of the excellent Montagu and other authors ought to be adopted. We do not understand the changing old accredited names for complimentary ones. This animal presents no essential difference from that of Pecten ; it is even difficult to appreciate the specialties, which only consist in the greater length of the three rows of the tentacular filaments of the mantle, which are long, close-set and numerous, of the various hues of pink and white. We have seen twenty of these animals alive; they exhibit the same character of the liver, branchiae, palpi, minute foot, pink ovaria, of most of the Pectines ; the ocelli in the minuter spe- cies are obsolete, but the rudiments of them are perceptible ; the same kind of locomotion in the so-called Lima, as in Pecten, I have frequently observed when placed in sea-water, in a shallow dish, and is effected by opening and suddenly closing the valves, with the posterior end in front, and thus rapid progress is made. When the adductors are unbent, the animal protrudes the mantle and mass of filaments, which then appear too large for the shell ; this is not so, as on the slightest disturbance all vanishes instantly within the valves. 54 PECTINID^E. The shell also only shows specialty-variations, the principal one being sometimes, not always, a more oblique outline ; in it we observe the same character of the ligamental and carti- laginous areas, a similar disposition of the longitudinal ribs, and the greater or less emargination of the valve under the posterior auricle, for the byssus, by which they are all fixed at some part of their existence, usually when young, and becoming often free when adult. With these views, I am compelled to consider Lima as a superfluous genus, and merge it in Pecten ; I cannot call the same animal both Lima and Pecten. The conchologists, perhaps some malacologists, will condemn these innovations ; but the knowledge of the animal configuration gives me the moral courage to perform the necessary amputations, for the benefit and safety of the system. This animal is rare at Exmouth at present, but was more plentiful some years ago ; it is, with its only two congeners, the P. Mans and P. subauriculatus, taken occasionally alive in the coralline districts. We have often seen it spin a byssus and fix itself. The animals of this section often collect and agglutinate in a mass minute nullipores, thus forming a nidus and harbour of refuge. The following Pectens have not been observed : P. NIVEUS, Macgillivray. P. niveus, Brit. Moll. ii. p. 276, pi. 50. f. 2 ; (animal) pi. S. f. 3. P. DANICUS, Chemnitz. P. danicus, Brit. Moll. ii. p. 288, pi. 52. f. 1, 2, 7, 8, 9, 10. P. ISLANDICUS, Miiller. Vide Brit. Moll. ii. p. 303. P. TIGRINUS, Miiller. P. tigrinus, Brit. Moll. ii. p. 285, pi. 51. f. 8-11. P. striatus, Brit. Moll. ii. p. 281, pi. 51. f. 1-4 ; (animal) pi. S. f. 2. P. obsoletus, Mont, et Turt. P.furtivus, nonnull. P. suBAUiucuLATus, Mont, et nobis. Lima subauriculatus, Brit. Moll. ii. p. 263, pi. 53. f. 4, 5. P. HIANS, Gmelin et nobis. Lima hians, Brit. Moll. ii. p. 268, pi. 52. f. 3, 4, 5; and (animal) pi. R. under the nainr of L. Icnera. L. lencni, Turton. OSTEEA. 55 OSTKEAD.E. One genus, with a single proteiform species, constitutes this peculiarly British family. Ostrea is the Lamarckian monomyal type. What has been said on the Anomiadce and Pectinida renders further detailed remarks unnecessary. We will only observe, though the general form of the branchial laminae is similar to those of the Pectines, that they are in their composition very distinct ; the complete absence of the byssal foot is another important deviation, and in other re- spects it is eminently distinguished from Pecten; Ostrea is generally fixed by the under or convex valve, and has, if any, a very limited locomotion, whilst Pecten is almost always free, and can perform the most rapid leaps and movements. OSTREA, Linneeus. O. EDULIS, Ibid. O. edulis, Brit. Moll. ii. p. 307, pi. 54, (animal) pi. T. f. 1. O. parasitica, Auct. Animal orbicular, subcompressed, of a pale drab colour throughout ; mantle thin at the beaks, gradually thickening to the ventral range, entirely open, except a short dorsal area, and has no trace of siphons or sessile apertures; the margin is not reflected on itself as in Pecten ; there are two rows of tentacular filaments springing from cord-like offsets of the margin; the front one is furnished with very thick, short, white, blunt cirrhi, disposed in a disorderly double line ; the other is more within the shell, and has a simple series of short, pale brown filaments of different lengths ; these are rarely seen exserted, from the habitude of the animal to keep the valves closed. The body, including the dark green liver with the incorporated cream-coloured ovarium, proceeds from the centre of the dorsal area on the anterior and posterior sides of the great subcentral muscle, at which point it termi- 5t> OSTREAD.E. nates. There are on each side a pair of simple branchiae that are without the reflected pouches of Pecten, nearly of equal depth, closely and conspicuously striated on both surfaces; they extend anteriorly to the palpi, but posteriorly only reach a little above the ventral range ; with them are connected around the mouth, by plain labial cords, two pair of subtri- angular, moderately long and large palpi, each plate being hung separately to the body, as in the ordinary Bivalves ; they are smooth on the outer surfaces, and well pectinated within ; the plates of each pair lie one on the other, but not being attached laterally, they do not double as a book shuts, or like those organs in Pecten. The body has not the rudiment of a foot ; the animal is, I believe, deprived of all locomotion ; Avhen the shell is not free, it is fixed by the under, which is the convex, valve. This species, when it inhabits the crevices of rocks, is sub- ject to great distortion; but the animal, though the shell forms a cylinder, or a right angle, or a disk, flatter than that of a P lacuna, adapts itself to these irregularities. There is but one British species, exhibiting infinite varieties, the effect of habitat and cultivation. The stomach contains the attritor or tricuspid appendage, that is worked by a short, grooved, elastic stylet, which, as there is no foot, has a resting-place in the upper part of the body. The intestine pierces the body to its fundus, then ascends, passing the heart without contact, which is one of the exceptions to the almost universal position of that organ in the Acephala; it then issues at the upper part of the dorsal slope, from which point it coasts in view, and is glued to the great adductor, terminating in a short, floating rectum nearly at the ventral level. The ovary appears to be amal- gamated with the body, and from April to July is continually discharging the ova into the branchiae, where they remain until they are ready to be replaced by another batch, and so on, until all are committed to their natural habitat ; then the animal recovers its exhaustion, and is edible about the middle of August, but is not considered fat and in full flavour until September. MYTILHXE, 57 MYTILID.E. We comprise in this family the genera Mytilus, Modiola, Crenella, Pinna, and Avicula. In coming to this arrangement we have had difficulties to contend with. At one time we were inclined, in consequence of M. Deshayes' remarks, to include Modiola and Crenella in Mytilus; but having very lately examined species of the three genera, we are by no means satisfied of the propriety of such a procedure. We think, from the configuration of the branchial laminae and the partly closed mantle in Crenella, it must stand as a genus. With respect to Modiola, our accounts of two of its species show that there are in them considerable variations : this cir- cumstance, with the pinnated character of the mantle in My- tilus and the differences of the branchial and anal mantellar terminations of the two genera, have made us hesitate to merge Modiola in Mytilus. The variations in the two do not perhaps amount to generic ones, and a coalition may even- tually take place. We have no difficulty in placing Pinna with the Mytili ; its animal in almost all points, particularly in the shape and position of the adductor muscles and internal nacreous aspect of the shells of the two genera, appears to support this determination. With Avicula we have greater hesitation ; but the recorded accounts by Poli, of the animals of that genus and Pinna, show such a similitude as to consti- tute a primd facie case for depositing them with the Mytilidcs. With these views, the family of the Aviculadee may be dis- pensed with. This location of Avicula must not be con- sidered as settled, even with reference to our method, for it is not improbable that it may have considerable alliance with the Ostread(B; but it is really immaterial as regards natural order whether it ranges with the Mytili or Ostrece, or constitutes an independent family, for in that case it must be fixed between the Mytilidce and Ostreadcs. We would recommend to naturalists a strict re-examination 58 MYTILID^I. of this family. We may have opportunities of again observing Mytilus, Modiola, and Crenella, but the animals of Pinna and Avicula are not met with on the South Devon coasts in my district of Exmouth; I should therefore be extremely obliged to malacologists who have opportunities of seeing these animals to communicate their remarks. I shall at pre- sent g;ive a short account of them from Poli, which I trans- o late from M. Deshayes' extracts from that eminent zoologist, in the last edition of Lamarck's ' Animaux sans Vertebres,' to enable naturalists to compare and weigh well their rela- tions with each other, and with the families of the Mytilidte and Ostreadce. MYTILUS, Linnaeus. M. EDULIS, Linnaeus. M. edulis, Brit. Moll. ii. p. 170, pi. 48. f. 1-4, and (animal) pi. Q. f. 5. M. incurvatus, M. pellucidus, M. subsaxatilis, Auct. Animal elongated, thick, subconical; at this season, 5th August, the general colour varies from white to all the hues of orange-yellow, except the foot, and the dorsal and ventral, posterior and anterior extremities of the mantle, which perma- nently exhibit the various shades of a deep reddish brown. The mantle is open from the very large, short, oblong oval, Avhite, simple membranous tube, situated on the upper poste- rior slope, which serves for anal purposes, and a separate branchial communication by a transverse fissure in the in- ternal septum into the ventral cavity, which, though it com- municates with the same common tubular process as the rectum, has no further connexion with the anal conduit. The mantle has a double margin, a plain outer and an inner one, which, from the point of the siphonal tube to the centre of the ventral range, is furnished with tentacular dendroid cirrhi, 15-25, of a pale brown on the main stems, with the ramose subfoliated fimbriae shadowing to pale yellowish white ; the remainder of the ventral range, in which the byssus and foot act, is only broken into long white dentations ; the two MYTILUS. f>!> margins are connected by short close-set perpendicular mus- cular threads, which act not only by the lines of junction, but also by a general subcircular contraction and dilatation of the fibres of connexion into a still closer or more lax union ; the effect of this combined action is to throw out and withdraw the tentacular fringes of the posterior lateral and ventral portions of the mantle; these vertical muscular lines also supply the adherence of the mantle to the margins of the shell, as in this species there are no longitudinal muscular bands emanating from the adductor muscles to support it. The foot is thick, fleshy, narrow, moderately long, proceed- ing straight from the heel, of an almost black-brown, marked with occasional lateral white lines; it produces coarse light brown byssal filaments from a groove at the posterior under part which is continued to the point ; the upper surface is plain, not grooved. The animal can detach itself from the byssus, by extracting and leaving it fixed to the substance on which it is moored, and in a very short time it is replaced by another ; this is the operation with the free My till. It is almost needless to remark that the great mass of these ani- mals are closely impacted in the sublittoral and laminarian districts. There are a pair of light brown branchise, of similar form, depth, and position, which run the length of the dorsal range, passing their diminished and well-fixed posterior ends into the branchial aperture; they are scarcely visibly pectinated on either side ; they also anteally diminish in depth, curving to the pair of palpi on each side the mouth ; they are connected by narrow labia, and at the basis with the palpi, which are long, very thick, triangular, pointed, of the same colour as the branchise, each having in the centre a raised line, probably an artery or branchial vein, from which they bevel on each side to a sharp edge, each pair folded together, being well striated within, not " partially," as is stated in the ' British Mollusca' on my authority, and plain on the outer surface. The liver is pale yellowish green, and granular. The crystalline stylet and stomachal attritor are present. The lateral dorsal secreting glands, which I believe produce the cartilage and a portion 60 MYTILIDJE. of the ligament, are well developed and of very dark colour. The body is the least I ever saw in so large a shell ; this is occasioned by the ovarium not being mixed up with it, but that organ is spread in great thickness over the major part of the inside of the mantle on both sides, and at the date above noted contains many hundred thousand ova, which at the latter part of the autumn are discharged into the sea, leaving the mantle a white thin membrane, after which the body of the animal increases in bulk and grows fat, becomes edible and in season, which is two months later than the oysters, as they are not considered good until the end of October. They are much eaten at Exmouth by the working people, but in some constitutions they have either a deleterious or the opposite quality, a pruriginous effect. It is a mistake that the ova are received in any part of the branchise for protection and maturation for some time pre- vious to ejection, as not one-tenth of the immense masses of the ovarian membranes could be located there; the branchiae, from their smoothness, are very ill adapted for such an asylum, and if they are ever seen there, it is from the unavoidable contact of the ova when in progress of exclusion : the pulli are never seen in the animal in a testaceous state, as in the fresh- water Unionidae, but are at once cast to the waves, where they become the prey of various animals ; still, enough escape de- struction to maintain their enormous numbers. The sea in autumn is filled with the ova : at ten miles from land in 14 fathoms water, if the fishermen's lobster-pots are left for two or three days, they will be covered with very young testaceous muscles, and in a week or two more than half an inch long ; but the parents never inhabit more than half a mile from the shore; of course the ova are floated out to sea, and sink as soon as they become testaceous. That the animal never carries testaceous pulli is manifest from its being more or less at all seasons edible. Though this is one of the commonest of the bivalves, it is an object of great interest to the mala- cologist from its elaborate organization. I may state that this is amongst the very few marine Acephala which have the ovaria attached more or less to both sides of the mantle ; by * t MODIOLA. 61 which it establishes a connection with the Anomiada, and perhaps in part with the Terebratulida. I am not sure that any other except Anomia is in the same category, and in that genus the ovary is only glued to the area of the mantle, which rests on the lower valve. MODIOLA, Lamarck. M. BARB AT A, Linnaeus et Auct. M. barbata, Brit. Moll. ii. p. 190, pi. 44. f. 4. M. Gibbsii, Auct. Animal elongated, thick ; mantle open, double-edged, with red-brown simple margins. The body is large, subrotund, brown ; from it springs a byssal foot, having a large fissure at its hinder part, from whence a fine bushy dark byssus issues ; the anterior part is finger-shaped, white, not long or pointed, with a longitudinal central depression. On each side the body are a pair of narrow branchial laminse, the upper not half the depth of the lower ; they are coarsely pectinated, and entirely coast the body, being brought close to the posterior extremity to receive the water. This structure of the branchiae is the substitute for the absence of tubes or any sort of siphonal fold of the mantle. The palpi are red-brown, long, flat, strongly striated transversely within, smooth on the outer surface. The shell of the present animal was 2^ inches transverse measure ; it was taken in the dredge in 1 5 fathoms water in a six-mile offing at Exmouth ; they are rare in that locality. M. TULIPA, Lamarck. M. tulipa, Brit. Moll. ii. p. 187, pi. 45. f. 7, and pi. 48. f. 6; and (ani- mal) pi. Q. f. 6. Animal elongated, body thick, pale red; mantle open, margin simple, plain, forming two very short, of the same length, scarcely separated pale yellow siphons, each fringed with about 20 close-set short cirrhi. Foot long, flattish, slender, with an intensely flake-white longitudinal line in the centre, having a byssal groove, increasing in depth from point to heel, from which, on its posterior side, a fasciculus of strong 62 MYTILID^E. filaments issues, by which the animal, wherever it may be placed, immediately attaches itself, and however frequently removed, refixes itself in a few minutes. On each side there are a pair of pale brown branchiae, narrow, linear, coarsely pectinated, but less on the inner than on the outer surface ; the palpi are short, pointed, triangular, and usually Lie rolled together laterally ; they are of the same colour as the branchiae, smooth within and strongly striated externally. This very elegant species is frequently taken alive in the coralline zone at Exmouth. It differs very materially in the organs from its congener M. barbata. M. MODIOLUS, Linnaeus. M. modiolus, Brit. Moll. ii. p. 182, pi. 44. f. 1, 2. M. phaseolina, Brit. Moll. ii. p. 186, pi. 44. f. 3, juv. M. Ballii, Brown. -, Brit. Moll. ii. p. 192. The M. modiolus and its young shell, styled by some M. phaseolina, are seldom met with on the South Devon coasts. The M. Ballii is of very doubtful British parentage ; we can refer to no figure ; and the animals of the first two have escaped our researches. CRENELLA, Brown. C. MARMORATA, Forbes. C. marmorata, Brit. Moll. ii. p. 198, pi. 45. f. 4. Animal suboval, thick, pale yellow ; mantle closed on the anterior ventral half, at which point is a large aperture for the foot ; the margin of the opening is plain, it is then closed, and forms a mixed purplish-red and flake-white membrane, which is produced into a small cylindrical anal tube, grooved at the base, with four or five minute dark cirrhi at the termination; and on its sides the mantle forms two pendulous puckered flaps of the same colour as the tube, with which the animal by bring- ing their margins into contact produces a canal, in conjunction with the groove, to convey the water to the branchiae. The foot is white, with a deep byssal groove, from which a strong CEENELLA. (53 filamentary mass issues, and fixes the animal to Ascidice and marine substances. The anterior part of the foot is white, narrow, finger-shaped, and moderately pointed ; when in full extension it takes the form of a narrow, flat tape, marked with a slight brown line running from base to point; it is pro- truded close to the anterior side of the byssus, but as an organ of locomotion it only comes into action when the animal is detached from its mooring, which it has the power of effecting by withdrawing the end of the byssal lamina from the groove in the heel, and it can refix itself by spinning a new byssus ; -this operation we have frequently seen ; when fixed, the foot appears to be an organ of tact, as it is often exserted, and the point kept in movement as if searching or feeling. There are a pair of branchial laminge on each side of the same size, and smooth on all surfaces ; the palpi are long, subtriangular, pale brown, and pectinated. The animal differs from Mytilus and Modiola in the perfect symmetry of the four branchial plates. This species is often attached to old bivalves and masses of Serpulce, but is more usually imbedded in the coriaceous mantle of the Ascidia mentula, from which twenty of all sizes have been extracted. It inhabits plentifully the coralline districts at Exmouth. We have not seen alive the following species : C. NIGRA, Gray. C. nigra, Brit. Moll. ii. p. 202, pi. 44. f. 5, and (animal) pi. Q. f. 7. C. DECUSSATA, Montagu. C. decussata, Brit. Moll. ii. p. 210, pi. 45. f. 2. C. RHOMBEA, Berkeley. C. rhombea, Brit. Moll. ii. p. 208, pi. 45. f. 3. C. DISCORS, Linnaeus. C. discors, Brit. Moll. ii. p. 195, pi. 45. f. 5, 6, pi. 48. f. 5. C. COSTULATA, RissO. C. costulata, Brit. Moll. ii. p. 205, pi. 45. f. 1. C. FAB A, Muller. C. faba, Brit. Moll. iv. Appendix, p. 256. Of the above, C. costulata is a variety of C. discors, though admitted by authors as a species. The C. faba, taken from a 04 MYTILIDJS. duck's stomach, shot in Northumberland, sub fide Kingii, is considered by him of doubtful British origin. We have the specimen. PINNA, Linnaeus. P. PECTINATA, Ibid. P. pectinata, Brit. Moll. ii. p. 255, pi. 43. f. 1, 2, and pi. 53. f. 8. P. ingens and P. papyracea, Auct. Animal elongated, body large ; mantle open, of delicate tex- ture except at the margin, which is furnished at the posterior end with two rows of tentacular cirrhi, but only one at its anterior portion. There are on each side a pair of large branchiae of nearly equal size and crescent-shaped, united by two wide labia, foliaceous on the internal surface, which fall on each side the body, connected with the buccal orifice and a pair of short, narrow, lanceolate palpi, which appear dispro- portionate for so large an animal. The mantle forms neither siphons nor even sessile orifices. The foot is conically sub- cylindrical, not long, with a byssal groove at the posterior bend, from which a large fine silky byssus of attachment issues ; this the animal has the power to discard when it wishes to change place, and can refix itself by spinning in a very short time a new one. Having only seen very young examples alive, we have for descriptive assistance had recourse to M. Poli, ' Test. Sicil.' AVICULA, Lamarck. A. TARENTINA, Ibid. A. tarentina, Brit. Moll. ii. p. 251 , pi. 42. f. 1, 2, 3, and (animal) pi. S. f. 4. Animal suboval compressed; mantle entirely open, having the margin fringed, as in Pinna, with tentacular filaments ; there are no siphons nor orifices. The dorsal range of the shell usually forms a slender linear posterior elongation, which is lined by a fold of the mantle. On each side of the body there are a pair of nearly similar-formed branchiae of crescent shape, ARCADE. 65 which around the mouth are united by two foliaceous labia, accompanied on each side by a pair of short palpi that on their free margins are obliquely truncate. The body is dimi- nutive in proportion to the size of the shell. The foot is small, subcylindrically conical, grooved at the posterior part, and emits a coarse byssus, which has all the active incidents of that of P. pectinata. We have been assisted in this account by extracts from Poli's ' Test. Sicil/ It appears then that Avicula scarcely differs from Pinna. We think that on comparison of the two genera, malacologists will be inclined to consider that their natural position is with the Mytilida. It may be in my power to supply a fresh description of Pinna, but extraneous aid will be required for Avicula, which has not occurred to us at Exmouth, though it has been fre- quently captured by the trawlers on the Plymouth ground. ARCADE. The Arcadce form a family of five genera, four of which, Area, Pectunculus, Nucula, and Leda, are so well characterized by animal distinctions, as not to require further remark ; we add a fifth, Galeomma, which, though an aberrant genus, we think we shall satisfactorily show has close relations with this family, wherein it is placed until the animal receives additional elucidation ; but this, from its rarity, may be far distant. It is to be regretted that near twenty years ago, when we had it alive for some days, we did not make better use of our oppor- tunities. Several observers have seen it, but, it appears, not with perfectly satisfactory results. Naturalists are earnestly invited to look after this elegant animal, and not fail to note at least its external organs and habitudes. Notwithstanding the uncertainty attached to this genus, we think its provi- sional residence in this family will become a permanent one ; - at all events, almost any position w r ill be more satisfactory than its present association with the Kelliadce. F 66 AKCAD^E. The family of the Arcada is the first, according to our method, in which the adductor muscles are established in their pyriform shape, similar size, and lateral position : the departure from the muscular disposition of the Ostreadoe, to the lateral one of the great mass of the bivalves, commenced in Mytilus, and has become complete in this family. Since the above was written we have added to this family a sixth genus, Lepton, under which head our reasons for this procedure will be found. ARCA, Linnseus. A. TETEAGONA, Poli et Auct. A. tetragona, Brit. Moll. ii. p. 234, pi. 45. f. 9, 10; (animal) pi. P. f. 1. Animal elongated, thick, white; mantle open throughout the ventral range ; its edge is plain, but the upper part of the posterior margin is marked, as in the Pectunculi and Pectines, with about 40 close-set, equidistant dark dots or ocelli, which become obsolete and vanish anteriorly ; the margin, or area within the ocelli, is mottled with pale yellow flake markings, which are also seen, though more faintly, on the under sur- face. The foot is white, and when at rest is bent, but, ex- serted, tapers subconically. There is a deep byssal groove at the posterior geniculated portion, for the green filamentous mass, which at the point of insertion into the cavity is split into two laminae; a neighbouring gland appears to supply a green glutinous fluid, from which the filaments are formed ; we conclude so, as whenever the byssus was extracted, the animal immediately produced from the fissure a flow of matter which almost instantly resolved itself into byssal threads ; and it is quite certain it can free itself from a state of fixity, which is effected by drawing the byssus from the groove, and entirely deserting it. This mano3uvre we have also seen performed by the animals of Area lactea and Galeomma Turtoni. There is little doubt that all byssus-bearing mollusca, when not con- fined in stony cavities, have the power of a limited locomotion by abandoning their moorings. The foot, independent of the deep fissure at the base for the ARCA. 67 insertion of the byssal lamina, lias a shallower continuation of it to the point. We have only seen the foot when protruded in a linguiform or subcylindrical shape, but it is probable that the longitudinal groove can expand and assume a spatulate character like that of Nucula and Pectunculus ; but the animal is very sensitive, and during a long examination never showed any kind of locomotion. There are on each side a pair of brown branchial laminae of nearly similar size, of small depth, which run quite horizontally; they are slightly crenated at the edges, and the outer surfaces are less striated than the inner. There are no pendulous palpi, but the linear branchiae are continued in a narrowed form on the buccal area, and meeting with their fellows, constitute expanded labia instead of strict palpi. Without entering into much anatomical detail, we may observe that the organs which supply the motive power to the circulation have a different arrangement in those Area which have the beaks widely separate; in them, there are on the medial line of the dorsal range two ventricles, each accompa- nied by an auricle, instead of, as in the ordinary arrangement, a single ventricle with an auricle, on each side : but this de- viation does not extend to all the genera of the Arcadae ; it appears to be the result of the distance of the branchial vein, on each side, from the motive power. In Pectunculus, in which the beaks are close together, and the points where the branchial veins pour the blood into the auricles are little sepa- rated, the ordinary structure of the single ventricle prevails. This species is very rare, but it has been taken by us more than once alive, in the coralline zone at Exmouth, in the sinuosities of masses of Serpulte that are deposited in old bivalves. A. LACTEA, Linnaeus. A. lactea, Brit. Moll. ii. p. 238, pi. 46. f. 1, 2,3. Animal oblong, thick, body white ; mantle pale red towards the middle of the dorsal range, entirely open, having the under surface of the ventral line marked with irregular flake-brown blotches on a pale yellow ground, and the upper, for some F2 68 ARCADE. little depth, with a sand-like rusty-brown belt, and a darker interrupted line nearer the margin, which is finely dentated ; but there are no equidistant points or ocelli, as in the last species. The mantle is without siphonal folds. The foot is white with a deep fissure at the bend, and is provided with a green filamentous membrane for attachment, which has all the same incidents as in Area tetragona. The foot is pure white, and can be exserted to a considerable length; it is fleshy, tapers cylindrically, and is very like that of Gaieomma. There are on each side a pair of similar-sized, very thin, pale yellow symmetrical branchiae, which gradually taper and unite around the mouth, forming a double lamina, of the same character as in Area tetragona and Pectunculus glycimeris. This species is frequently taken free in the dredge, in the coralline zone at Exmouth, and also fixed by the byssus amongst the masses of Serpulce in old bivalves. We had in our possession the identical Area barbata first introduced as British by Dr. Turton in his ' Conchylia Di- thyra/ and, on showing it to Dr. Goodall, he expressed an opinion that it was an exotic specimen. We have not seen alive the A. RARIDENTATA, Searles Wood. A. raridentata, Brit. Moll. ii. p. 241, pi. 45. f. 8. PECTUNCULUS, Lamarck. P. GLYCIMERIS, Limiseus et Auct. P. glycimeris, Brit. Moll. ii. p. 245, pi. 46. f. 4, 5,6,7 ; and (animal) pi. P. f. 6. Animal suborbicular, lentiform, bluish white ; mantle open throughout the periphery of the shell, except the dorsal line ; the margin is plain, having its upper surface for the depth of an eighth of an inch powdered with minute sand-like, pale red, brown or black points. There are at the posterior side, for half its length, at the verge of the mantle, about twenty- five minute equidistant black dots or ocelli, besides short, brown, transverse bars; the under surface is marked with short flake-white cross-lines. The mantle has neither tubes nor PECTUNCULUS. NUCULA. 69 orifices, but under the posterior termination of the branchiae there is a very short anal duct issuing from the body, with a small round reflexed margin. The foot in the live animal is snow-white, without a byssal gland and groove, but deeply cloven in the longitudinal line of its base to effect a subdiscoidal extension ; it springs from the centre of the basal portion of the body; when in full action it ranges anteally and posteally, forming an elongated suboval disk at the central portion, and tapers at each end to a moderately pointed termination ; when the foot is not fully protruded, it forms three or four folds at the margins; the animal does not execute a direct progressive locomotion, but only turns the shell round on its disk, or from side to side. There are on each side a pair of symmetrical branchise of the same size, which, instead of having the transverse striae or circulatory vessels linear, present the appearance of white wavy ringlets, and are crossed by other sinuous lines ; both surfaces have much the same depth of markings. The branchial laminae hang very obliquely, and from the smaller or anterior extre- mity a pah 1 of very narrow, light brown, linear labia or palpi, smooth on both sides, originate, and pursue their course around the mouth, and meet with the fellow pair. In their linear form and drooping position, these appendages much resemble the labia or palpi of Nucula. This species is frequently taken alive in the dredge in the coralline zone at Exmouth. We observe a close alliance be- tween Pectunculus and Nucula ; both have the same sort of suboval foot disk, and a similar quality of progression ; and the linear connecting branchial palpi greatly resemble each other. NUCULA, Lamarck. N. NUCLEUS, Linnaeus. IV. nucleus, Brit. Moll. ii. p. 215, pi. 47- f. 7, 8 ; (animal) pi. P. f. 4. N. decussata, Brit. Moll. ii. p. 221, pi. 47- f. 1, 2, 3. N. radiata, Brit. Moll. ii. p. 220, pi. 47. f. 4, 5, and pi. 48. f. 7- Animal suboval, thick, having the ventral portion of the body mottled flake-white ; the liver is dark green, with the 70 AKCAD^E. snow-white ovarium attached to it, full of ova in July. The mantle is open from the anus to the buccal aperture, its margins plain; there are no tubes, not even an orifice, but the rectum terminates within it by a simple perforation in the body. There are two branchial laminae on each side, brown, of an elongated triangular form, and fixed horizontally; the broader part of them is at the short truncate or anterior end of the shell, from whence they gradually taper to the posterior termination, close to the debouchure of the rectum ; the upper lamina, which is contrary to the usual plan of those organs in most of the Acephala, is by far the largest, and entirely envelopes the under one of similar shape ; they are finely striated on the outer surface, but more visibly on the inner. There are two labia or pendulous appendages on each side ; the one nearest to the anterior end of the branchiae hangs vertically, the upper part of it being of a white, elastic, coriaceous substance as far as the middle, when it changes into a transversely striated brown narrow leaf-like lamina, the half of which is longitudinally doubled on the other portion ; the second labium, or that nearest to the buccal orifice, coalesces with its counterpart on the other side, encircling the mouth, and then accompanies the other, on the same side, in a pen- dulous direction to the ventral region; it is long, linear, coarsely transversely striated as its fellow, and has also the one hah folded on the other. This is a very singular struc- ture of these organs, but the foot exhibits a still greater de- parture from the ordinaiy forms of that organ; it is pale yellow, of a regular oval form, deeply serrated at the margin into about fifty denticular points; one-half the disk when within the shell lies folded on the other, but when in action it becomes a flat subcircular disk ; the motion of the animal, though progressive, is not direct ; it turns round as on a pivot, and its path describes an irregular ellipse. The animal is shy, and requires continual attention to observe these manoeuvres. This species is extremely common alive in the Exmouth coralline region. Conchologists have exercised their ingenuity in convert- ing some very trifling varieties into distinct species. The NUCULA. LEDA. 71 N. radiata of authors is beyond doubt the " nucleus," and so is the N. decussata. We have examined the animals of the three, and they are absolutely identical. The Exmouth variety of the " nucleus," termed " decussata," does not attain so large a size as the Irish examples, but I challenge the most acute observer to point out an essential conchological variation ex- cept the one stated. N. NITIDA, Sowerby et Auct. N. nitida, Brit. Moll. ii. p. 218, pi. 47. f. 9. The organs of this species are similar in essentials to those of the N. nucleus. We may state, the specific distinctions are, that the foot is of much paler colour, and the disk less deeply dentated; the branchise are paler and smoother on the outer surface, but more striated on the inner, than in the N. nucleus. It inhabits in company with its congener, but is twenty times more rare. N. TENUIS, Montagu. N. tennis, Brit. Moll. ii. p. 223, pi. 47. f. 6; (animal) pi. P. f. 5. We have not seen it alive ; it is a Scotch production. LEDA, Schumacher. L. CAUDATA, Donovan et Auct. L. caudata, Brit. Moll. ii. p. 226, pi. 47. f. 11, 12, 13; (animal) pi. P. f. 2. Area minuta, Auctorum. We can say little of this genus except that it appears to differ from Nucula in having the mantle produced into two siphons of moderate length, partly united, but bifurcating at their terminations. We have only rarely taken the dead shells of this species at Exmouth. It is an abundant Scotch pro- duction, and differs much in the outline and markings. L. PYGM^A, Minister. L.pygmeea, Brit. Moll. ii. p. 230, pi. 47. f. 10; (animal) pi. P. f. 3. This species, if distinct from the L. caudata, is unknown to 72 us; we believe it has only occurred in the Hebrides. We doubt the distinction. GALEOMMA AND LEPTON, Turtoii. The genera Galeomma and Lepton have received from the hands of Dr. Turton a conchological constitution, but as respects natural position, they have been buffeted from place to place, in accordance with the various views of naturalists. In some systems they are associated with the Kelliadte, though doubtfully, on account of the want of knowledge of the animal. These disturbing causes are happily in a great measure removed, and we have it in our power to fix permanently these wanderers in the only British family that has with them a sufficiently corresponding community of attributes. Though they are aberrant genera of the Arcadan type, when strictly consi- dered they undoubtedly belong to that family, and it will be shown that they have the strongest claims to this their natural lineage. To establish a new family for these beautiful genera would indeed be a superfluous labour, and repugnant to our well- known feelings to add unnecessarily to a host of worthless positions, when there is already an unmistakeable resting-point. But our descriptive notes will further explain these matters. GALEOMMA, Turton. G. TURTONI, Sowerby. G. Turtoni, Brit. Moll. ii. p. 105, pi. 36, f. 1 1 ; (animal) pi. O. f. 5. Animal oval, fleshy, pure white; mantle of thin texture, except at the edge, which is muscular, and forms a tumid cord that extends beyond the shell, from which are thrown off undulated double margins, one of which lines the shell, and is marked with equidistant frosted-white eminences or ocelli, eight or nine on each side, with fine white filaments between them. The mantle is partly closed in front, but there is an anterior pedal aperture. The foot is long, cylindrically taper- ing to its termination ; at the heel, close to the body, is the GALEOMMA. 7.3 byssal fissure, from which a fasciculus of fine filaments issues, which fix the animal so firmly to whatever it is placed on, as to require some force to detach it ; in fact, the hyssus is discarded by being altogether withdrawn from the slit in the foot whenever an attempt is made to remove the animal by force; but though we repeated this operation several times, the little creature did not appear to be injured or less lively, but as soon as it had crawled to some distance, we had the good fortune to witness the formation of a new byssus, which was effected by the discharge of a light green glutinous opake matter from the fissure at the heel of the foot, which by its ponderosity resolved itself into delicate fibrous filaments that instantly adhered to the saucer: we detached the animal several times, the byssus was always left, and a new one formed. On leaving it for the night, in a marked position, we found in the morning that it had detached itself by aban- doning the byssus, and formed another at a considerable distance. The animal marches with great vivacity, by flattening the valves into the form of a circular disk ; it then, by the foot, aided by the muscular margins of the mantle, makes rapid progression. We are unable to speak of the branchiae, or the particular character of the palpi or labia, and whether they are distinct free pendulous palpi, or the drooping folded labia of the NuculcR', nor is it clear, from M. Mittre's or Dr. Philippi's account, which of the two forms is the true one. I blame myself greatly for my inattention to these points when I had it in my power to verify them ; they have now become important, either to support or impugn my reasons for placing Galeomma in the family of the Arcadte. But if even the palpi or labia should show a difference from the usual structure of those organs in the Arcad<&, it must be considered as an aberration of an aberrant genus ; however this may be, abundance of facts will be adduced to justify the removal of Galeomma to the Arcada. My memory will not allow me to say anything of the siphonal apertures, or of the long anterior stylet. We have twice taken this beautiful creature alive in the coralline zone off Budleigh Salterton, Devon. 74 AKCAD.E. It will be observed in the account of this animal, taken from notes made twenty years since, that the mantle is partially closed in front ; this is the only point against the Arcadan position, as in the typical species that organ is open through- out the ventral range. We certainly did not then observe so critically as now ; there may be an error ; the animal requires further investigation, which we confidently believe will confirm our present views. Galeomma, by the contiguity of the beaks and very limited ligamental central facet or area, together with the minute glossy circular porcellanous nuclei of the umbones, is closely allied to Pectunculus, also, perhaps, more so to Area, particularly A. tetragona, by the linear character of the hinge and ligament, which has the central portion semi- internal, and is carried on each side to the termination of the dorsal line, being throughout as straight as in Area ; the impressions of the adductor muscles scarcely diifer in the two, and there is in both the same dull scabrous irregularly nodose aspect of the inside of the valves. The ventral gape in the regular specimens of A. tetragona is similar in Galeomma. The character of the striae or minute ribs is the same as in Area lactea, except that in it the bifurcations are seen inter- nally, whilst in Galeomma they are external. With high powers, the oblique, though nearly obsolete teeth may be observed on the ligamental line, and the internal linear areas are similar to those in A. tetragona and P. glycimeris. Many other minute similitudes may be mentioned, but enough has been advanced to show that the conchological indices decidedly fix Galeomma with the Arcadce. Let us speak of the internal organs. The foot in Galeomma is byssal, and precisely of the same form and character as that of A. tetragona. As a last, but, as we think, very convincing proof of the relation of this genus to the Arcadae, are the regular equidistant frosted-white eminences or ocelli, which, except in colour, entirely resemble those in the typical Area ; and as there are no other genera but the Arcae and Pecten in which the mantle of the animal is furnished with ocelli, it follows, from the entire difference of the position of the ad- ductor muscles in Pecten and Galeomma, that this species, on LEPTON. 75 malacological considerations, can belong to no other family than the Arcadce. LEPTON, Turton. L. SQUAMOSUM, Montagu. L. squamosum, Brit. Moll. ii. p. 98, pi. 36. f. 8, 9 ; and (animal) pi. O. f. 6. Solen squamosus, Auct. Animal inhabiting a very flat, subrhomboidal, white, porcel- lanous, punctured shell ; its ground colour is a clear white. The mantle is very large, having the margins sinuated, often puckered into two or three folds at the will of the animal ; they extend beyond the shell more than one-third of the ver- tical measure at its centre, from which springs a row, on each side the middle of the ventral range, of twenty-five rather long, slender, milk-white tentacular pointed filaments; but the mantle thus clothed is only protruded largely beyond the shell, from the middle of the anterior side, throughout the ventral range, to the same level as the posterior end ; from these points to the umbones it is never seen, being either closed or not protruded, but its suture or edges are furnished with about forty long, strong, blunt, frosted-white, rather close-set cirrhi varying in length ; a part of these range at the posterior side of the beaks, above the sessile anal orifice, which occupies a small space without cirrhi, between the termination of the protrusion of the margin and the commencement of the larger filaments on the broader, larger, and posterior side ; of that part of the filaments at the anterior side of the beaks, one is thicker, broader at the base, and double the length of the others ; this is the last of the larger ones, which at one time I thought was tubular and might be an oviduct, but further examination seemed to disprove this idea. None of the fila- ments show much motion ; the long one only, when the animal advanced a step, made an arcuated contraction, similar to that of the fore-finger in extenso when quickly brought down to the palm of the hand; it then resumed the straight position to await another step : all the other cirrhi are either retractile or contractile, separately or en masse. 76 ARCADE. The foot is hyaline azure, with a broad longitudinal medial line of intense snow-white, and a still intenser flake at the anterior end ; it is fixed to the centre of the body by a mode- rately long pedicle; on first protrusion it takes a vertical position, and has a linguiform tapering aspect, but this part almost immediately, after feeling about, ranges itself anteriorly and horizontally ; and at the same time, on the other side of the pedicle, a bevelled, attenuated, pointed portion issues, somewhat shorter than the first ; this is longitudinally cloven as far as the pedicle, and can form a sort of oval disk, but on the march it is rarely expanded : at the base of the cleft is the byssal gland, which occasionally pours out a glutinous red filamentous matter, that in confinement is copious, and discharged anteriorly, which at first I thought was faecal matters, and was puzzled to account for such an issue anteally, but the subsequent view of the single sessile posteal anal conduit and the ejection of pellets cleared up the difficulty. This foot is in every respect similar in miniature to that of the Pectunculus pilosus and of the Arcadoi, and in no other bivalve family does the foot exhibit a similar structure : this singular pedal characteristic of itself would sufficiently confirm the natural position of Lepton and Galeomma. The animal is vivacious, and allowed itself to be examined many times daily ; it marched with quickness, but I only once saw it progressing in a vertical position ; the usual posture of the shell is to rest on one of the disks, which is frequently changed for the other ; the adductors did not appear to allow of a greater opening of the valves than the ordinary extent. The animal, when placed at the bottom of a glass, always crawled up and moored itself by a filament at the side ; some- times, however, it slipped its moorings and floated free on the surface of the water with the umbones downwards, and after an interval refixed itself by spinning a byssal thread. I cannot speak at present of the branchiae and palpi, as the animal and shell are in my collection, and are thus preserved to show that the shell, though usually described by concho- logists as gaping, can, in consequence of the flexibility of the thin laminar valves, be completely closed. There is no LEPTON. 77 branchial siphon ; but there are mantellar folds, which, with the great ventral opening, amply provide for the admission of the water. The animals of this interesting group exhibit, in the tenta- cular filaments and curious foot, as well as in the sculpture of their shells, very considerable variation from KeUia rubra and Kellia suborbicularis, the types of one of the genera of the family in which they have been located by authors, doubtless from the want of knowledge of the animal. Taking into consideration that the Leptons have many of the attributes of the Arcades, and especially giA'ing due weight to the re- markable similarity between the foot of Lepton squamosum and the Pectunculus pilosus, I am almost induced to believe that it is in a false position, in connexion with the Kelliadce, and that it ought to follow or precede Galeomma, which, with me, is an undoubted genus of the Arcadce. The punctures of this species and of L. convexum are in the test ; with respect to its congener, the L. nitidum, it has been stated that it is smooth and without punctures : this is a mistake, as I can show fifty specimens not only well- marked on the greenish epidermis, but in the substance of the shell. I have the satisfaction to state, that I have observed another live L. squamosum, and also obtained full notes of the animal of one of our great desiderata, the L. nitidum, from a most lively animal, which for several days gave me every facility for examination. The L. squamosum, just alluded to, was kept thirty-four days in a glass of sea- water, changed daily, and was apparently as vigorous as when first placed in captivity ; it thus appears that the Conchifera can exist for a long time in pure sea- water, on the animalcules it contains, though that aliment may not be their sole resource in freedom. I may observe, that the habitude of crawling and swimming with the foot uppermost in Lepton, and in several other minute bivalves, perhaps in all, shows the close alliance of the Acephala with the Gasteropoda, all of which, in their minute condition, have precisely the same peculiar system of dorsal natation. I ought to have mentioned that the liver is light green and 78 ARCADE. mixed up with a flake- white ovary; but from the extreme tenderness of the branchiae, I cannot speak of them and the palpi with certainty as to form and number. July, 1852. As I had just finished the above, a lively specimen of this species was met with, which, on being placed in water, at once unfurled its long and beautiful fringes, and exserted the ample niveous mantle and foot. This is certainly the Prince of British bivalves ; the snow-white colour of both animal and shell sheds over this interesting creature the in- expressible charms of purity and elegance. It now lives in the same vase with its pigmy congener, the L. convexum. L. CLARKITE (nova species), Clark. L. Clarkia, Brit. Moll. iv. p. 255, pi. 132. f. 7- L. testa fragili, obliquo-subovali, compressa, postice et antice rotuudata, albida, mediocriter nitida, striis concentricis, confertis, tenuibus notata; apices minutos, prominulos, subtilissime punctatos gerente. Latus rostris anterius, quoad longitudinem transversam, duplo posterius superat. In valva dextra, utroque, dentes laterales, duplices, distantes apparent ; in sinistra, simplices ; inter quos, utra- que valva, dens unicus, primarius, erectus, acutus, oritur. Mensura obliqua -TJ-, transversa y^, altitude aut crassitude ^ uncise. Zonam corallinam Devoniae meridionalis, prope ostium Iscae, rarius habitat. Animal ignotum. Of this minute and elegant species, a series of eighteen perfect specimens have occurred, and having compared the hinge and dentition with forty examples of the L. convexum and L. nitidum, I can state that there is not the slightest variation in this respect in the three species. Its distinguish- ing characters are the almost perfect obliquely oval shape, being without a trace of the subangularity which is invariably seen at both extremities of the congeneric Leptons; and, as to the punctures, it is more devoid of them than the glabrous varieties of the L. nitidum, which, however, in the forty spe- cimens I possess, all show more or less the punctured aspect on the umbonal area ; but in the L. Clarkia only the apical circumscribed space is in some, but not in all examples, almost LEPTON. 79 invisibly punctured, which condition is rather more pronounced within than on the outside of the apices. At one time I almost thought that the L. nitidum and L. convexum might march together as a single species, subject to many varieties ; but an increase of my series of both has, at least for the present, made me doubt the propriety of considering the two as identical. The animal of the L. con- vexum is still unknown, and until it occurs, a safe determina- tion on these points cannot be made. The animal of the L. nitidum I know well, having in the last summer observed two examples for four days; it only differs in some minor peculiarities from the L. squamosum, one of which I kept in sea-water thirty-four days, when it was killed whilst still vigorous, in consequence of my departure from the sea-side. I may state, that in L. Clarkice the concentric strise of increment are close-set and sharp, and sometimes broken into very short waved streaks ; these in some of the specimens are crossed by gently raised lines of an intenser snowy-white than the general colour, which radiate sparingly from the beaks to the basal margin. This delicate species cannot be confounded with any of the minuter bivalves : by its hinge it is essentially a Lepton : the nearest approach to any other species is to the Montacuta bidentata, which differs in form, colour, and fragility, and in having the lateral dentitions almost close together, without the primary teeth between them ; instead of which, there is a minute moveable ossicle, convex on one side and concave on the other, as in the Anatince or Thraciee ; this locks into a sloping pit that has sometimes the appearance of being ridged, which is only due to portions of the ruptured ossicle adhering to it ; but in Lepton the primary teeth are persistent or integral parts of each valve. Fresh examples, new facts, and further investigation have all but convinced me that L. convexum and L. nitidum are distinct. Our Leptons, which I name according to rarity, will stand thus : 1st, L. convexum; 2nd, L. Clarkice; 3rd, L. nitidum ; 4th, L. squamosum. One of the distinguishing marks of the new species has been already alluded to, the oblique rounded outline ; but another 80 ARCADE. equally important is, that the side anterior to the beaks is double the transverse length of the posterior one ; whereas in all the other Leptons, of which I have more than a hundred examples, the beaks are nearly central, and they have more or less subangularity at the sides ; therefore the oblique outline, rounded sides, and position of the beaks, are unerring guides to distinguish the L. Clarkits from its congeners. The animal has not been observed. L. CONVEXUM, Alder. L. convexum, Brit. Moll. ii. p. 102, and iv. p. 255, pi. 36. f. 10, mag- nified. L. nitidum, Turton et Auct. Kellia nitida, Brit. Moll. ii. p. 92, pi. 36. f. 3, 4. The animal inhabits a light greenish-yellow or pure white, subrhomboidal, moderately convex, more or less punctured shell. The mantle is frosted- white with the margins plain, but as much proportionately protruded beyond the edge of the shell as in L. squamosum ; it is in like manner clothed with cirrhal filaments of about the same length, and of pruinose white, but unlike that species, they are rather less developed dorsally than ventrally ; each filament at its terminal edge is studded with four or five white points or cilia, so sharp and minute as to require a powerful lens to see them. There is no conspicuous leading process, as in the preceding species, but the mantle, at the same anterior point, forms a visible pro- jection or fold. In this species, and contrary to L. squamosum, the longer and broader end is anterior, but the beaks are so central, that there is little difference in the sides ; the single sessile anal tube is exactly as in the last species ; there is no branchial siphon, the water enters at the extensive ventral aperture. The foot is almost in every respect similar to that of its congener ; it is perhaps larger in proportion, of pale azure hue, marked with intense but irregular flake-white minute blotches; the posterior extremity is as long as the portion anterior to the pedicle ; its termination is perfectly aciculate, and like its congener deeply grooved as far as the junction with the body, at which point is the byssal gland, LEPTON. 8' and the superabundant filamentous matter is similarly dis- charged. The L. squamosum is a lively creature, but this, not one- third of the size, is far more active, creeping up a glass as easily as a Gasteropod ; but the posterior portion of the foot is not expanded; perhaps in freedom it is deployed on the march ; in confinement both shell and foot are carried laterally. The liver is light green, united to a flake-white ovarium, now, in June, full of ova. Transverse length |, vertical T ^, dia- meter -Jj of an inch. It would appear that this species in every essential is identical with the L. squamosum, and it settles the position of the yet undiscovered L. convexum. This is the first record of this rare animal that has appeared. Exmouth, June 20, 1852. I have this day the pleasure to state, that the problem is solved as to the identity or distinctness of the Lepton nitidum and L. convexum by the capture of a live specimen of the latter, having the shell sculptured with the rough and intensely marked characteristic punctures of that species. On putting the animal into water it instantly deployed its organs ; and for their description I have only to refer to the preceding account of the L. nitidum, which in future will take the appellation of a variety of its old associate. The two are so identical, that after ten days' examination I can make no alteration in the minutes, except the having seen the animal march on the disk of the foot, more than once, with the shell in a vertical posi- tion ; it has all the same habitudes as the L. squamosum, and of course differs in no respect from its smoother variety, the late L. nitidum. It is now alive, and probably by changing the water daily it will live as long or longer than the L. squa- mosum mentioned above. It is therefore evident that the punctures of this species are very variable, ranging from the most minute granules that scarcely interrupt its smoothness to the coarsest sculpture. As the specific appellation of nitidum is obviously improper, the more significant one of convexum ought now to be adopted. Since the above was written I have taken two examples, one this morning (July 18), of the smoothest variety of the ' con- 82 vexum,' late the 'nitidum'; both are in the vase with the highly- punctured one captured 20th June last, now quite vigorous, in company with the L. squamosum alluded to as taken 2nd July ; this capture has given me the advantage of a live examination of the two completely opposite conditions of the ' convexum' whereas the one above was only referable in comparison with an account of a live ' nitidum ' taken last year. And I can again state that the two varieties are identical. I give another proof of identity. I have just (1852) taken alive a curious example, that shows one half of each valve finely punctured and the other grossly granular. LUCINLD.E. This family has only one genus, Lucina, which includes about eight species. Live specimens of the typical L, borealis are of rare occurrence ; w r e have met with none for forty years on the Devon coast, and of the L. rotundata only a small example has been examined. Nor have the animals of the L.flexuosa and L. ferruginosa been seen by us, but we receive them sub fide Forbesii et Hanleyi. Since this was written, it will be seen below, that fortune has been favourable, and enabled us to fill up some of the gaps in the species of this family, but the curious incidents attending it are so largely noticed in the descriptive history as to dispense with further remarks. LUCINA, Bruguiere. L. ROTUNDATA, Montagu et nobis. Diplodonta rotundata, Brit. Moll. ii. p. 66, pi. 35. f. 6 ; (animal) pi. M. f. 7. The present account of the species was written at Exmouth, in the summer of 1849, and the reason of noting the date will shortly appear. Animal lentiform, moderately thick ; mantle plain, some- LUCINA. s:i what closed anteriorly and posteriorly, leaving a large pedal opening in the centre of the ventral range ; no siplional pro- cess appears, not even an orifice ; the branchiae must be sup- plied through the pedal aperture. The body is very small, pale brown, with the intestine passing through the liver. There are two subquadrangular branchiae, and two palpi, on each side ; the former are finely pectinated above, and smooth on the under surface ; the palpi are moderately long and pointed, as well as striated on one side ; both are of a good brown colour. The foot is clear white, moderately long, flattish, and lanceolate-shaped laterally and at the point. The L. rotundata has been consigned to a new genus, termed Diplodonta, by the learned authors of the ' British Mollusca/ on our authority as to the animal structure. I feel pleasure that they state this allocation is provisional, as the animal presents anomalies of so peculiar a nature, that malacologists are earnestly called on for a minute examination of this curious creature. I accept the invitation, and hope either to confirm my observations, or offer rectifications. This species has many of the characters of the type, L. borealis, and I think, whether my notes are confirmed or not, it must be considered an out- lying branch of this family. The hinge and other distinctions will not, in any case, allow of the suggestion of handing over this species to the Kelliadce. Fresh, though dead shells are commonly taken in the coral- line zone at Exmouth, but I never met with more than two specimens alive ; the one examined was less than half an inch diameter. The following addenda were made at Exmouth on the 22nd July, 1850, a year after the preceding notes. The account in the ' British Mollusca/ vol. ii. p. 65, of the Diplodonta rotun- data, our Lucina rotundata, was made from the sketch above. The possession of a live specimen of f of an inch diameter, enables me to say that my account, as far as it goes, is nearly correct ; but I can offer some amplifications, particularly on that important organ the foot. Beyond all doubt, I state, that there are, on each side, a pair of branchiae and palpi ; the branchiae are transverse, though somewhat elongated, G 2 84 LUCINID./E. subangular laminae, sinuated at the margins, pectinated, and fixed, as is usual, to the dorsal range, the upper plate being little more than half the depth of the lower one. The palpi are short, pointed, pectinated, and subtriangular ; they lie on each other, and I may say, that neither of these organs present any remarkable variation from the usual rim of the Acephala. The liver on the dorsal range is of an intense black -brown granular substance, with the ovary mixed up with it, more anteriorly. There are no siphons, but only a short pendulous rectum, which is a very minute cylinder, discharging by what I considered to be a crenulated slit in the mantle high up in the posterior dorsal range. If I am mistaken as to the slit, which possibly may have been an accidental lesion, in that case it would discharge within the walls of the mantle, and finally eject from the central pedal aperture, which is a large opening commencing from the posterior closure of the mantle to the anterior adductor muscle, situated very low, near the anterior ventral range, from whence the mantle becomes closed to the anterior dorsal range ; therefore there are only two apertures in the mantle, the small posterior slit, for the ejection of the excessively minute faecal pellets, and the very large ventral opening for the foot. The possession, as yet, of only one good-sized specimen has not enabled me to speak positively as to the existence of the anal fissure, but beyond doubt there is neither anal nor branchial siphon. The foot is a most curious organ; it is characteristic of the typical Lucinte. It proceeds from the centre of the body, and represents a long, lax, flat, rugose, annulated, retractile hose, with a wrinkled, elastic, clavate continuation or off- spring, with slight shoulders to the terminus, which appears to be perforated ; this latter, somewhat club-shaped portion, when in quietude, folds on the penultimate part, and the whole lies within the mantle. It is difficult to conceive how a flat, lax, strap-shaped, tubular pedal appendage should in action suddenly assume the appearance of an elongated, arcu- ated, pointed conical foot, as is represented in the figure of the 'British Mollusca/ which, however, cannot be improved as to actual appearance when the foot is exserted, except LUCINA. 85 to show a minute terminal perforation. This metamorphosis is probably effected through its elasticity, and being distended with water. In the large specimen, of which this is the de- scription, the animal was more apathetic than the small one of the first part of these notes ; the foot was never protruded, and of course no siphons, as none exist ; the only movement for forty-eight hours was a central opening to admit the branchial water, and the exsertion of the margins of the mantle, which are quite plain. We have here the decided foot of the typical Lucince, agreeably to the descriptions of M. Poli and M. Valenciennes ; but if the latter is right as to there being but one branchial lamina on each side, in all the true Lucinte, our present spe- cies, which beyond doubt has two on each side, would be an aberration from the typical Lucina, though so closely allied to it by the foot, which is of so singular configuration, that we think it a generic characteristic of far greater value than the single branchial plate on each side, which form prevails in all the Anatinae, and in some of the Tellina. We therefore would prefer to place this animal as a Lucina, even if it should turn out that all the Lucince have but one branchial lamina, which fact at present is by no means to be depended on ; we consider the character of the tubular foot to be more worthy and important, in this case, than that of a singularity in the structure, or rather in the disposition, of the respiratory organ; and as to the branchial plate being a single one, it is more so in appearance than in reality, which is fully explained in the notes on Anatina phaseolina. In this very delicate animal we could not trace the connection of the foot with the viscera of the body, if it exists. M. Valenciennes says, that the water from the foot must enter and mix with the splanchnic con- tents ; we greatly doubt this fact, and refer for our reasons to the preliminary observations on the Lamellibraiichiata. L. BOREALIS, Linnaeus. L. borealis, Brit. Moll. ii. p. 46, pi. 35. f. 5, and (animal) pi. M. f. 6. Exmouth, 2nd June, 1852. This day a live specimen, about fths of an inch diameter, 8fi LUCINID-E. was met with, close in shore, at Littleham Cove. Though im- mediately put into water no organ was exserted, except at the centre of the ventral range a small portion of a pointed foot. As the animal continued apathetic it was opened, when a large corrugated subcylindrical foot became visible, which on being divided proved to be tubular, but near the body it appeared slightly geniculated. On each side there was one rather elongated branchial plate, apparently divided by the branchial artery in two portions ; these were connected and doubled on each other, forming one thick plate, of a darkish brown colour, shot with a hue of pink, very closely and strongly decussated by the branchial vessels. No palpi were seen. The liver is brownish-green. The margins of the shell are plain, and the edges of the mantle loosely sinuated. The posterior adductor scar is pyriform, the anterior one narrow and strap-shaped. Of the two primary teeth in each valve, one of each is cloven ; there is also an anterior lateral one in both valves. Another specimen has this year (1853) occurred, of the same size, and at the same habitat. It proved lively, and has enabled me to offer some additions and explanation. The foot is very narrow but lancet-pointed, and when fully ex- tended is nearly as long as the vertical measure of the shell ; it is always in the first instance exserted from the ventral central point, and from thence can move itself anteally to a right angle. It is transversely and longitudinally wrinkled, and when alive has the aspect of being roughly shagreened ; when dead it appears intensely corrugated across and length- ways ; it has a decided heel near the junction with the body, and is beyond doubt tubular to within a short distance of the termination, and possibly may be entirely perforated. I made with the scissors two sections before the tubular structure was visible, but in so delicate an organ the pressure of the knife might close a real perforation, which I believe exists ; not to admit water either to the branchiae or viscera, as some natu- ralists think, but to render the foot a potent locomotive organ by inflation, and having the power of opening and constricting the perforation for the issue and admission of the water. The LUCINA. 87 mantle is slightly dentated, and open from the anterior ad- ductor throughout the ventral range to near the posterior muscle ; it is then closed by a knotty stop,, and a linear fissure is visible, I presume, for the dejections, and then the mantle is finally closed. Nothing is ever protruded beyond the shell except the foot. The water must reach the branchiae from the ventral range. There is certainly on each side the mouth, a short, coarse, thick, subcylindrical, striated palpum, and I am not sure that there are not a pair on each side. The only action of the animal was the exsertion and retrac- tion of the foot, which is well represented in the ' British Mollusca,' pi. M. f. 6. This species is the type of the genus. L. FLEXUOSA, Montagu. L.flexuosa, Brit. Moll. ii. p. 54, pi. 35. f. 4. Exmouth, 2nd June, 1852. Animal inhabiting a white, irregularly globular shell, Avith a longitudinal posterior furrow. It was apathetic, and pro- truded no organs. On being opened, the plain-edged mantle showed only one anal fissure. In the middle of the ventral range lay a long corrugated cylindrical tubular foot, which appeared capable of great extension ; it made its way through the body to the branchiae, and there threw off vessels, right and left, which appeared to communicate with those organs, so that it would seem that the foot performs both the functions of a locomotive, and is a vehicle to convey water to the branchiae, in lieu of the usual posterior siphon ; and it is pro- bable that throughout the genus Lucina the foot performs this double duty. There is only one thick branchial plate, as in L. boygalis, doubled on itself, of a red-brown colour. No palpi were detected. The liver, formed of two minute leaf- shaped light green granular masses, curiously lines the body and part of the foot on each side. This animal was taken in company with the L, borealis above described, close to the shore, at Straight Point, Little- ham Cove, near Exmouth. 88 KELLIAD.E. The undermentioned references have not occurred on the South Devon coasts. L. SPINIFERA, Montagu. L. spinifera, Brit. Moll. ii. p. 49, pi. 35. f. 1. L. LEUCOMA, Turton. L. leucoma, Brit. Moll. ii. p. 57, pi. 35. f. 2, as L. lactea. L. FERRUGINOSA, Forbes. L. ferruginosa, Brit. Moll. ii. p. 60, pi. 34. f. 1, magnified. L. DIVARICATA, Linnseus. L. divaricata, Brit. Moll. ii. p. 52, pi. 35. f. 3. KELLIAD^. This group of minute bivalves has lately been distributed in five genera, Kellia, Montacuta, Galeomma, Lepton, and Turtonia, but the four latter are so generically discordant with Kellia (proper), the type, that we may say they have no connection with it. We have therefore, without hesitation, removed Galeomma and Lepton to the Arcada ; Montacuta, for one of its species, to the new family of the Montacutida ; and Turtonia, for its only species, to another new family, the Turtoniadce ; under which heads our reasons for these changes will be found. The lately acquired knowledge derived from an examination of all the Leptons except L. Clarkice, impera- tively requires a family rectification ; they have not the vivi- parous and tubular specialties of Kellia, and exhibit such other different characters and structure as fully to sanction the junction of Lepton with Galeomma, and the removal of both to the Arcades, Again, with respect to Montacuta, we have relieved it of one of its late members, by consigning the M. bidentata to the Anatinidas, as by the testaceous moveable ossicle it certainly belongs to that family, which we confidently think will obtain another recruit in M. ferruginosa ; that is, if it should be found to have the characteristic ossicle of the tribe. The Kelliada, therefore, in our method, consists of only one genus, Kellia (proper), with two species. KELLIA. 89 We digress, and for the second time earnestly recommend naturalists to observe, in sea-water at least, the external organs and habitudes of the minute animals of all genera, bivalve and gasteropodan, for little more can be done from their minuteness, and publish notices of them in our natural- history records; not mere names and habitats, as is too often the case, but their peculiarities. Opportunities of meeting with rare live animals do not often occur; we speak from forty years' experience ; none ought to be passed by, and all should be examined without delay; the interval of even an hour often paralyses the animal functions : let our motto be " carpe diem ;" many rare creatures, from its neglect, have been lost to science. The almost total dismemberment of the Kelliada is the moral of the above ; we wish to impress the necessity of a more careful examination of the minuter Mollusca. We ought to state that the true Kelliadae have the hinge furnished with variable minute irregular primary teeth under the beaks, with flattish triangular laterals on each side in each valve, those of the right one being obscurely double, and a long, strong, very oblique, white internal cartilage, which is often ruptured into two parts, one of which lies in each cartilage-pit. KELLIA, Turton. K. SUBOBBICULARIS, Montagu. K. suborbicularis, Brit. Moll. ii. p. 87> pi. 18. f. 9 and 9 a, 9 b; and (animal) pi. O. f. 4 and 4 a. Animal suborbicular, pure white ; the mantle may be termed partially closed, though there are three openings in it ; the ventral one is considerable, and serves for the admission of water to the branchise, and as an issue for a small hyaline linguiforrn byssal foot, which usually lies centrally exserted, to be prepared to act anteally and posteally ; it is also at the anterior or shorter end, to which the beaks curve, produced into a conical entire tube, not divided within, almost as long as the shell, plain at the orifice; this anomalous production is, 90 KELLTAD^E. as far as we know, confined to this species and Kellia rubra ; the third orifice in the mantle is a small sessile anal one. We believe the water to aerate the branchiae enters by the pedal fissure, and when used, is expelled therefrom ; it is possible that the curious anterior tube, which is a continuation of the mantle, may, in conjunction with the central opening, also admit some water to the braiichise ; but we will observe on this point by and by. On each side of the body there are a pair of narrow, symme- trical, pale yellow, striated laminae, and correspondent pairs of short, thick, strong, subtriangular, coarsely striated palpi ; the liver is pale green, and in close connection with the ovarium, which is a thin membranous sac full of ova in the genial season. It is now proper to inquire into the probable uses of the anterior anomalous tube. As there is no ostensible reason why nature should have departed from her accustomed plan to place that organ before, which in every other bivalve except K. rubra and this is behind, we cannot rationally conceive that this singular appendage is a special branchial tube, as the pedal orifice is most ample for the entry and expulsion of the aerating fluid; we therefore think the following facts will afford malacologists assistance in determining its functions. Whilst examining some K. suborbicularis, my attention was suddenly attracted by observing several testaceous young ejected from the anomalous tube; these I collected and have them now by me. Notwithstanding tliis fact, I have never, until lately, been able to discover, in any of the numerous ovaria I have inspected, anything except ova in different stages of advancement ; but it is exceedingly probable that the shells I saw ejected may have been deposited in tliis tubular appendage of the mantle, and there received the development in which I found them. Since this was written, I have to state subsequent facts resulting from the examination of a very large Kellia suborbi- cularis. I placed it on the umbones, when it immediately exserted and opened the tube ; by the aid of a powerful lens, I counted at its fundus fifteen largely developed ova, and I KELLIA. 91 have no doubt that this animal and that of K. rubra are furnished with these unusual appendages to minister as organs of reproduction. I have further to state, that on submitting the animal to my scalpel and one of Mr. Ross's microscopes, I received the fullest confirmation of my conjectures, having found in the ovarium, resting on the fimdus of the tube, ova in advanced conditions, together with fully-formed testaceous young. I have carefully preserved the ovarium. Therefore this species, like K. rubra, is undoubtedly viviparous : the only difference between the two is, that one of the young phases of K. rubra is greatly matured in the ovary, and only requires the open tubular fold as an oviduct, and to convey the water to the pulli, which, from their position high up on the dorsal range, could not receive the ambient element without such an appendage, whilst the K. suborbicularis has the tube entire, as it is for some time a nidus for the young before exclusion. I have also to add, that on opening a very large K. sub- orbicularis, I found the contents of the ovarium converted from its usual ova-like aspect into many thousands of com- pletely testaceous young, to be further developed before their issue from the anterior tube or oviduct, without which the water could not well be conveyed and retained for the use of the young. The reason why this state of the ova has so long escaped detection is, that the ovarium has not been examined at the proper season. To see it as I have described, we must attend to the injunction of Lucretius " Athens et terrse genitabile quserere tempus." K. suborbicularis, though often taken free in the muddy deposits of old bivalves, is also found in the crevices of the triassic rocks at Exmouth, in company with the Saxicava and Pkoladts, in which it rubs out a kind of cell, and thus becomes entitled to enter the category of the boring fraternity ; it is attached by a byssus, not merely thread-like filaments, such as the freer ones throw out when placed in a saucer, but a decided membranous white hyaline byssal lamina, which cannot be detached without some force ; it always parts from the animal and is left in the cell ; if it is placed in Avater 0-2 KELLIADJi. in a piece of hollowed-out sandstone rock, it will produce another : of these facts we speak with certainty. This species, when imbedded in the crevices of rocks, is more globular and of firmer texture than those which are found in the muddy deposits of old bivalves, taken in the coralline districts, six miles from the shore ; these are very thin and almost mem- branous at the umbones, of larger size and subtriangidar figure, and have the tube marked with flake- white longitudinal lines that are not apparent in the thicker varieties. Having examined many of both these variations, without detecting a difference in the organs, we must consider them as dependent on habitat. K. RUBRA, Montagu. K. rubra, Brit. Moll. ii. p. 94, pi. 36. f. 5, 6, 7 ; (animal) pi. O. f. 3. Animal suborbicular, white; mantle partially closed and with only two apertures ; the anterior is the anomalous tubular projection, which is not entire as in K. suborbicularis, but slit open at the base, and serves as a passage for the foot. When the animal marches it is generally pushed therein, displacing the sides of the scission, which on its withdrawal assumes the aspect of an entire tube. This combined pedal aperture and tubular appendage is divided by a septum from another con- siderable fissure in the mantle, from which the points of the branchiae are visible; through it the water to supply the vital principle reaches them, and when effete is expelled by the channel at which it entered ; the anus is a sessile orifice completely within the slit of the mantle, and discharges therein; in fact, the fissure is the entrance of a common cavity that serves to admit the branchial water and receive the rejectamenta before exclusion. The anterior tube being nothing more than an open protrusion or continuation of the mantle, some water may reach the branchiae through it, and be expelled therefrom in combination \vith the strict pedal aperture ; but its principal use, as we have shown in K. sub- orbicularis, is to act as an organ of reproduction to convey water to the pulli in the matrix, which from their dorsal posi- tion could not well receive it without the aid of such an KELLIA. 93 appendage, which also serves as an oviduct. We have omitted to say, that when the faeces are received within the mantle, they are instantly ejected in light yellow or greyish cylindrical pellets. In this respect there is a difference between K. sub- orbicularis and K. rubra; in the former the anal orifice is protruded in a trifling degree externally, in the latter it is within the mantle. The foot is broad at the base, long, linguiform, and has the termination rather rounded than pointed; its bluish-white hyaline texture is marked from base to point by a dull intenser flake-white line. When in a basin of sea-water, it at once attaches itself by thread-like filaments that issue from a distinct byssal fissure. The foot when exserted, but not in action, occupies a central position; it usually progresses anteally by being pushed through the anomalous fold of the mantle, and fixing itself by a species of suction, is drawn forward by muscular contraction with much vivacity, and it can also in a more limited manner progress posteriorly. The animal never remains long without forming a byssal attachment, but has no difficulty in slipping its cable when inclined to move, which is always discarded, and when required another is bent. The dark liver and yellow ovarium are situate high in the dorsal region; the latter in the genial season contains from 10-20 or more fully-formed testaceous pulli, and at the full time, the viviparous colony are ejected through the tubular fold of the mantle. In a parcel of animals examined in the winter, the ovarium contained no young ; I therefore presume that ' ' Alma Venus" does not influence the self-sufficing loves of these Mollusca until " species patefacta est verna diei, Et reserata viget genitabilis aura Favoni." A review of these notes, and a comparison of them with those of K. suborbicularis, will, I think, prove that this species and its congener are nearly similar in organs, habitudes, and functions, with slight variations of specialties, and that they form a well-defined small genus which I believe only contains the two species that are described. 114 MONTACUTID.E. The habitat of this singular creature is at a far greater elevation in the littoral zone than any other bivalve, and nearly as far removed from the sea-water as the Littorina petraa, which in many positions is never completely sub- merged. These minute bivalves are plentifully imbedded in the Lichina pygmaa, and in the higher levels exist for weeks, without complete immersion ; they are consequently deprived of regular branchial currents, which in this case can only have a very limited operation, as in even the most favourable levels they must be deprived of sea-water for very many hours out of the twenty-four. We presume, that when these animals are in elevated positions, the tides washing the bases of their rocky habitats, combined with the saline mixture of floating atmospheric particles, supply sufficient humidity for the sus- tentatioii and well-being of these singular bivalves. MONTACUTID^, Clark. Notwithstanding our disinclination to create new families, we have no choice but to constitute the Montacwtida, though it be for only a single species, the Montacuta substriata, a late sojourner of the Kelliadce. It has little in common with Kellia (proper), except a partial resemblance in the structure of the hinge and presence of a byssus, but it differs essentially in the absence of the singular and anomalous anterior tubular processes, and the probable want of a viviparous reproduction. With Lepton and Galeomma, both former members of the KeUiadce, now of the Arcades, to which we refer, it has nothing in common but having a byssus. With Turtonia, also removed from the Kelliadce, it cannot be associated, from the hinge-teeth and internal long linear white cartilage, as in that genus the hinge-ligament is strictly external, and the teeth are altogether of a different composition. No existing genus or family can receive M. substriata without violence to natural order. Therefore, as we have undertaken a new arrangement of the Kdliadae, we are bound, as far as possible, in the reconstruction, to march with malacological rigour. MONTACUTA. 95 The only set-off to our chagrin in being compelled to form two new families is, that they will acquire a lasting fame by their titles, in conjunction with the present generic ones, by ministering double honours to two of the most eminent British naturalists, Montagu and Turton. We have already, in our preliminary remarks on the Kel- liad(E, accounted for the disposal of the Montacuta bidentata, formerly of this family, by its transference to the Anatinidae ; and we now state that the third and last member of Monta- cuta, the M. ferruginosa, Brit. Moll. ii. p. 72, pi. 18. fig. 5, 5 a and 5 b, is consigned to the company of its congener, for the reasons stated under Anatina. MONTACUTA, Turton. M. SUBSTRIATA, MoiltagU. M. substriata, Brit. Moll. ii. p. 77, pi. 18. f . 8 and 8 a; (animal) pl.O. f. 2. Animal suboval, thick for its size. It has an oblique out- line, the longitudinal measure being greater than the trans- verse ; the body and mantle are pale yellow, the liver dark green; the mantle has a simple margin, and is largely open ventrally for the passage of a hyaline foot, that has a byssal groove at the heel, from which strong coarse filaments issue, and attach it to the ordinary habitat, the spines of the Spatangus purpureus : all the observed specimens were thus attached, and could not be removed without injuring the animal or shell. They were cut off by scissors, and on being placed in a watch-glass of sea-water immediately protruded the large foot, far exceeding in length the shell; it is mus- cular, raised in the centre, bevelled on each side to a fine awl- shaped edge, and tapers to a very rounded termination, not showing a trace of the lanceolate point. Locomotion would appear to be incompatible with the apparently fixed habitat, but it, as well as the other byssal bivalves, has the power, which we have seen them exercise, of changing place. When the animal marches the foot is extended, and its rounded ter- mination is instantly fixed to the vase in which it is deposited; 96 TURTONIAD./E. then by the retractor muscle it is drawn forward, making such rapid progression as to cross a watch-glass in a minute, and on the passage turns itself several times by a twist of the foot from side to side. No siphonal processes, nor even a simple orifice, were observed. When opened, the large foot is the most prominent object; with a good lens the byssal fissure is distinctly visible. Though there are traces of a branchial lamina, we could not detect its configuration, nor the presence of palpi. In the hinge, under the beaks, there is a minute obsolete primary tooth or two, with only a single compressed triangular lateral, in both valves, but on the longer side only, which is the anterior one. This structure differs much from Kettia. Some malacologists call what we term the lateral teeth in Kellia and this genus, the cardinal ones ; but as in them there is no moveable ossicle, we consider the minute denticles at the edge of the cartilage-pit, directly under the beaks, the primary ones. But the case is different in those minute species styled by authors Montacuta bidentata and M. ferruginosa ; these have been removed by us to the Anatinte, as they have the characteristic ossicle of the family ; in them there are no minute cardinal teeth, and what in Kellia and Montacuta are termed laterals, here become of cardinal value. TURTONIAD.E, Clark. We have been obliged to establish this family for Turtonia, with a single genus of only one species, planted by authors in the Kelliadce, though it has not the slightest community of attributes or structure with any of the genera of that group. Lepton, Galeomma, Kellia and Montacuta are as far asunder from it as the poles. We mention a convincing proof of its heterogeneity : in all the species of those genera, excepting perhaps Kellia suborbicularis, in which the sides are nearly equal, the shortest is the posterior one; but in Turtonia minuta the longest is posterior, and it is the only animal of these tribes that has a considerably produced anal siphon. TURTONIA. 97 TURTONIA, Haidey. T. MINUTA, O. Fabricius. T. minuta, Brit. Moll. ii. p. 81, pi. 18. f. 7 & 7 ; (animal) pi. O. f. 1. Mya purpurea, Montagu et Auctorum. I have never seen this animal, and can only record the slight notes of authors, that the foot is very large, strong, genicnlated, and issues from the shorter end of the shell ; the mantle is largely open anteriorly, and a slender somewhat produced siphonal tube proceeds from the longer side. The shell, except in contour, in many respects agrees with the Lucince. The ligament is external, and there are in perfect specimens two cardinal teeth ? in each valve, one or both is often bifid ; the teeth vary much from being deeply cloven ; and thus in some examples the appearance of two, three, or four is presented, and in old shells they are otherwise con- fused and indistinct. The pallial impression is entire; the anterior adductor cicatrix, as in many of the Lucince, is rather more extended and at a lower level, but not much more, than the posterior one. Under the microscope we discover traces of the vertical lines so conspicuous in the margin of Lucina bore alls ; and we may also state, it is thickened, dull, and somewhat chalky in some specimens. The slender tube also allies it with that section of the Lucmte which have a produced anal conduit. The foot, when exserted, has the ordinary tongue-shaped aspect of most of the mimiter bivalves, but that is no proof that it has not the singular tubular structure characteristic of the Lucinee, as even in the type L. borealis and in L. rotun- data, both of which beyond doubt have the true Lucinidan foot, it shows no trace of the singularity when protruded, probably from being inflated with water to produce tension. It is only when the animal is killed and opened that the curious con- figuration of the pedal organ is seen. We do not mean to say that Turtonia is a true Lucina, or even one at all, but merely mention these facts, which may have the value they deserve. But we will endeavour to obtain this animal. All these con- H 98 CAEDIAD^. siclerations appear to support us in having transferred this species from the Kelliadae to a separate family. It is well to mention that the figure referred to of this animal is incorrect, from the engraver having placed the foot and siphon at the wrong ends ; the position of each should be reversed. CARDIADJ3. A family of only one genus, of nine species. This is a well- marked group by its radiating ribs, which are either nodose, spinous, or vaulted, with interstitial furrows of transverse waved striae. The tubes are short or sessile, but in some species an imperfect pallial siphonal sinus may be seen. The animal is distinguished from every other bivalve tribe by the extraordinary length of the subcylindrical geniculated foot, and by the external surface of the siphons being clothed with long pendulous filaments. CAKDIUM, Linnaeus. C. ECHINATUM, Linnaeus. C. echinatum, Brit. Moll. ii. p. 7? pi- 33. f. 2. Animal suborbicular, pale yellow; mantle open, with the margin slightly dentated, pale brown, forming a branchial and anal siphon, which are | of an inch long, in a shell of about an inch-and-a-half vertical and transverse measure ; they are of a dirty white hue, united or soldered on each other, and have not the aspect of a single sheath ; the anal is rather the shortest and smallest, and protrudes a plain globular valve at its termination; each is fringed with about 15-20 white cirrhi, having at their bases short, dark yellow, and minute close-set brown lines, which give the orifices of the siphons the appearance of being encircled by a fine line, and on the external surface of each there are long, somewhat curved white filaments, which also for a short distance clothe the mantle above and below them. The foot is subcylindrical, CARDIUM. narrow, geniculated, and of flesh colour, the result of a deli- cate and easily obliterated epidermis, under which it is pure white ; its length is at least twice that of the shell. There are a pair of semi-oval branchiae on each side, the upper one being as long as the lower, but not half the depth of it ; they are pale brown and well-striated on the outer surface, but less so within ; the palpi are of the same colour, very long, slender, pointed, with decided raised vessels on the inside, though less marked externally. We subjoin a separate account of the young shell, which is the C. ciliare of authors, and has been considered as belonging to the C. aculeatum ; but having had opportunities of exami- ning large suites of both species of |th of an inch to 2| inches diameter, we can confidently state that it is the young of this species. C. ECHINATUM, JU11. C. ciliare, Auctorum ; Brit. Moll, (animal) pi. N. f. 4, as C. echinatum, jun. Animal suborbicular ; the specimen examined was fths of an inch diameter, pale yellow ; the mantle is muscular, and coarsely dentated at the edge, which character in a great measure disappears in the older shells ; it is open throughout, forming short tubes, the branchial one having about sixteen short cirrhi and minute red points at the base ; the anal siphon has the usual tubular retractile process and twelve cirrhi, which also have red points at the base ; besides the siphonal cirrhi, there are above and below and on the tubes a few coarser white filaments, which are invariable appendages of all the Car dia. There are on each side the body a pair of pale brown roughly striated suboval branchial laminae, the upper being much narrower than the under ones; the striae are apparent on both surfaces; the corresponding pairs of palpi are long, narrow, subtriangular, pointed, and rather more strongly striated on the inner than on the outer sides ; they are pale brown. The foot is very long, at least double the vertical measure of the shell, subcylindrical, narrow, pointed, angulated, and of a pale flesh colour. H 2 100 This species is taken abundantly at Exmouth, of all sizes, in the coralline zone. C. EDULE, Linnseus. C. edule, Brit. Moll. ii. p. 15, pi. 32. f. 1-4; (animal) pi. N. f. 5. Animal suborbicular ; the body is large, subglobose, and of an opake Avhite; mantle pale yellow, edge fringed. The siphonal apparatus forms two short conical tubes, separate from their bases, and divergent; the branchial has ten long white cirrhi, with two or three intermediate shorter ones springing from the orifice, which is encircled by a dark or red-brown line; the anal tube has a similar line, but no cirrhi; it is provided with a retractile tubular valve ; both tubes have on their surfaces the usual characteristic curly white filaments, and they vary from whitish to pale yellow or red- dish-brown. The foot is considerably smaller than in any of the other Cardia, and has very little of the long cylindrical aspect of that organ in its congeners, being rather flat and lanceolate ; its colour varies from opake white to pale brown or yellow. There are a pair of moderate-sized, pale brown, suboval branchiae on each side, finely pectinated, the upper one being much the smallest ; the palpi are red-brown, longish, pointed, flat, and subtriangular, smooth on the outside and pectinated within. There are many varieties of this common species which result from habitat; they are sometimes excessively thin, arising in certain estuaries from a more than usual affusion of fresh with the salt water, and under those conditions have been named by some naturalists C. rusticum. It is proper to observe, that the true Limisean C. rusticum is a very different species, which has long been known to collectors, though misnamed C. tuberculatum, the strongest and most ponderous of all the Cardia. The young of one of the varieties, from its umbonal transverse bands, has been mistaken for our C. fas- datum, the C. elongatum of some authors, but the oblique out- line of the latter species will always distinguish it from any of the young fasciated varieties of C. edule. CARDIUM. 101 C. FASCIATUM, Montagu. C.fasciatum, Brit. Moll. ii. p. 25, pi. 32. f. 5 ; (animal) pi. N. f. 3. C. elongatum, Auctorum. Animal suborbicular, body flake- white ; mantle plain. Si- phoiial tubes not exserted usually above Jth of an inch; of the same length, united, each with ten simple white cirrhi, and on them are the invariable filamentous appendages. The foot is long, naiTOw and subcylindrical, or finger-shaped, and, contrary to the Car diet in general, hyaline. The branchise are subsemicircular, pale brown, the upper one not half the size of the lower, strongly striated on the outside and smoother within; the palpi are very short, triangidar but pointed, striated on the outer, and much less on the inner surface. The liver is green and very anterior ; the ovarium white, and full of ova on 4th of August. It inhabits the coralline zone, and is rare at Exmouth. C. NODOSUM, Turton. C. nodosum, Brit. Moll. ii. p. 22, pi. 32. f. 7- C. muricatulum, juv., Auctorum. Animal subglobose ; mantle open, edged with white pointed filaments issuing from the points of the mantle corresponding to the ribs. The siphons are pale yellow and very short, each with ten or twelve flake-white cirrlii at the orifices and red points at the bases, with the addition of the curved white filaments above, below, and on the tubes; the anal one pro- trudes the usual retractile valve. The foot is white, mode- rately long, subcylindrical, and slightly geniculated. There are a pair of semi- oval branchiae on each side, the upper is not half the length and breadth of the under one ; they are strongly pectinated on the upper, and less on the lower surface; there are two very small triangular palpi on each side, pectinated in a similar manner with the branchiae. This species, at Exmouth, is only met with in the coralline zone, but it is not uncommon. We have ascertained by a comparison of the C. muricatulum of authors, of sizes of less than y^th-y^ths of an inch dia- 102 CARDIAD.E. meter, with the animals of the C. nodosum, that they are identical. If it had been our practice to generalize,, the singular same- ness of the organs of this genus would have authorized a departure from the plan of detailing the specialties of every case : the present work is not intended to be subjected to the dull and heavy labour of being doggedly read through con- secutively; we consider it one of particular reference, and think that Ave have done good service to the reader in stating the specialties at length in nearly every case. C. NORVEGICUM, Spengler. C. norvegicum, Brit. Moll. ii. p. 35, pi. 31. f. 1, 2; (animal) pi. N. f. 1. C. Iceviyatum, Auctorum. Animal thick, suboval, elongated, the vertical measure exceeding the transverse; the mantle is closed throughout the posterior range, and at its lower part forms two short siphons united at their bases and divergent at the extremities, of a pale yellow, marked with flake-white spots and lines ; the branchial tube is rather the shorter, but of greater diameter, and is rarely extended more than half an inch; its orifice is circled with twenty long yellowish-wliite cirrhi, having dull red-broAvn markings around their bases; the anal siphon is simple, and has the usual retractile valve, which is marked on the lower and upper surface with a faint red-brown line, and points of the same colour at the termination. The siphons and the posterior range are clothed with thick-set pale reddish- brown and pale yellow curved filaments. The mantle, from the point where the filaments terminate, is simple and open, with its outer and inner margin of a flesh colour, and affords a passage to a long, powerful, geniculated, cylindrical foot, that has a pointed termination ; its substance is rigid, and, except the white point, of a red flesh colour, which the slightest touch removes and shows the white ground ; it is longer than the greatest measure of the shell, and its epidermis appears shagreened and marked with anastomosing fine lines. There are on each side a pair of pale brown suboval branchiae, with the margins of a deeper bro\vn ; the upper one is considerably CAKDIUM. 103 smaller and of less depth than the under one ; they hang more vertically than those of its congeners, and the transverse pectinations are more conspicuous without than within ; the palpi are very long, triangular, united by a labium around the mouth, and with the branchial laminae by a membranous filament; they are more strongly striated on the inner than on the outer areas. This elegant species is frequently obtained by the dredge in the coralline district at Exmouth. The following species have not occurred to us alive : C. RUSTICUM, Linnaeus. C. rusticum, Brit. Moll. ii. p. 11, pi. 31. f. 3, 4. C. ACULEATUM, Lmnseus. C. aculeatum, Brit. Moll. ii. p. 4, pi. 33. f. 1. C. FYGMjEUM, Donovan. C. pygmaum, Brit. Moll. ii. p. 2.9, pi. 32. f. 8 ; (animal) pi. N. f. 2. C. SUECICUM, Reeve. C. suecicum, Brit. Moll. ii. p. 33, pi. 32. f. 6. The last may be a young delicate var. of C. edule. MACTRIDJ3. This is one of the old Linnaean families, with only a single genus, so distinctly characterized as to require few remarks ; it contains four British species. By its open mantle and short tubes it is allied to the Veneres, but we cannot concur in the opinion of some authors, that it presents many features of the Myadae. We take the liberty of saying, that it will be very difficult to find a single accordant point between the two families, except the generalities of every bivalve. Mactra and My a are far asunder : the former has the mantle open, short tubes, and very circumscribed in length, suboval, broad branchiae ; in the latter, the branchiae are narrow, elongated, with a part of them lying in the branchial tube ; the mantle is quite closed, and the siphonal apparatus particularly long. The dentition of the two families is entirely different, with the 104 MACTKID^E. exception of the V-shaped tooth in Lutraria, which genus in our method belongs to the Myadas. MACTRA, Linnaeus. M. STULTORUM, Linnseus et Auct. M. stultorum, Brit. Moll. i. p. 362, pi. 22. f. 4, 6 j and pi. 26. f. 2. Animal suboval, of the palest bluish-white; mantle open throughout the ventral range, its edge is clothed with a de- licate intensely white fringe of short filaments ; both siphons are short, of the same length, united, covered by a fine brown deposit, which appears to be independent of the epidermis on the shell ; the united tubes are never exserted more than half an inch, their orifices are fringed with simple dirty pale red cirrhi; the branchial, which is the longest, with 12-16, the anal has 14-20. The lower part of the body is white, and the dorsal range, containing the brownish-green liver and ovarium, of a dull opake white. The foot is thick, long, bevelled to a sharp margin, and extensible from all the phases of obtuseness to the pointed lanceolate extremity. There are on each side the body two suboval, brown or drab-coloured branchiae, the upper the smallest, and obliquely very finely striated by the vessels of the circulation. The palpi are long, triangular and pointed, of an opake brown, more distinctly pectinated than the branchiae, particularly on the inner sur- face. It has been omitted to be stated that the anal tube is provided with an exsertile hyaline valve, and our experience positively entitles us to say, that the anal tube of almost every bivalve is usually furnished with that appendage, the use of which is doubtless to regulate the entry and issue of the water, which has probably a communication with the ovarium, as well as for other functional purposes, which are alluded to in our remarks on the Pholadidee, in the section on the branchial currents. This tubular retractile valve is never attached to the branchial siphon; at least we can bring no instance of its presence to our recollection. This is a littoral animal, and often, after a gale, is abun- MACTRA. 105 dantly cast on the Warren Sands, at Exmouth, from whence we obtained our finest specimens. M. SUBTRUNCATA, Da Costa. M. subtruncata, Brit. Moll. i. p. 358, pi. 21. f. 8; and pi. 22. f. 2; (siphons) pi. L. f. 3. As the external organs of the Mactrce are very similar, it will only be necessary to mention the variations of some of the succeeding species from the M. stultorum, which may be considered the type of the genus. The present animal differs in having no fringe to the margin of the mantle, at least none could be detected ; the siphons are united as in M . stultorum, and clothed with an evanescent epidermis ; the orifices have simple pale red, white or yellow cirrhi ; and we may conclude our account by observing, that the branchiae and palpi are of a pale brown, and that the foot is of a paler yellow, narrower than in its congener the M. stultorum. We have in this instance, and one or two others, departed from the usual plan of a detailed description ; it is an example of the inconvenience attendant on the omission, as we are here obliged to have recourse to our notes of another species to complete the present one. We think, if possible, such references should be avoided. M. SOLIDA, Linnaeus. M. solida, Brit. Moll. i. p. 351, pi. 22. f. 1, 5; (siphons) pi. L. 2. M. truncata, Brit. Moll. i. p. 354, pi. 23. f. 1 ; and iv. p. 253. The animal, like the M. stultorum, has the margin of the mantle fringed; the siphonal canals, as to structure and arrangement, are the same as in the two former species, and of a pale brown colour; the branchial one, w T hich is the largest, has about sixteen, and the anal twenty, shorter pale yellow, or brown, or reddish cirrhi at their orifices, which vary greatly in different localities. The branchiae and palpi differ from the preceding animals in being of a deeper brown, with a decided reddish hue ; otherwise they are of the same shape, and nearly with similar pectinations. The M. solida varies in shape in every locality ; in some it is flat-sided, tumid, and 106 MACTEID^l. triangular; in others, compressed, sharp at the sides, and transversely produced, which variations have caused even the excellent Montagu to err in the creation of his M. truncata from one or other of the varieties of the M. solida or of the M. subtruncata. Without being positively certain, we think the M . truncata of authors must be expunged as a species ; and whether it be a synonym of the M. solida or M. sub- truncata is doubtful; at any rate, all the shells that have been as yet shown us are referable to one or other of these species. The contour of the M . solida, which is taken abundantly at Exmouth at low water, in the sandy ranges adjoining the Mare rocks, is of the tumid and subtriangular variety : it is from this locality that Dr. Turton obtained the types of his M. crassa. M. ELLIPTICA, Brown. M. elliptica, Brit. Moll. i. p. 356, pi. 22. f. 3 ; (animal) pi. L. f. 1. Animal suboval, compressed ; body flake-white ; liver green, scarcely visible, being covered by the opake white tough dorsal skin ; mantle open, very slightly fringed anteally, plain pos- teally ; siphonal tubes in a specimen f of an inch transverse by | an inch vertical measure, are not exserted more than |ths of an inch, and appear as if enveloped in a sheath; each orifice has about twelve cirrhi at their bases, below which a bright orange line encircles the sheath, which is of pale yellow. The branchiae are light orange, subsemicircular, the upper being much smaller than the lower, and very finely pectinated. The palpi are long, narrow, pointed, pale brown, and more conspicuously striated than the laminae. Foot white, rather large, muscular and lanceolate, by the aid of which the animal turns its shell, with great ease, from side to side. This species appears distinct, and though it is difficult to define distinctions by the organs, which in all the Mactrae. are so similar, still there is a delicacy and elegance in the appear- ance of this creature which almost assures us that it is not a dwarfish variety of the M. solida, which at Exmouth is strictly a MACTRA. 107 littoral species, while the M. elliptica is never taken, except by the dredge in the coralline zone, six miles from the shore. M. HELVACEA, Chemnitz. M. helvacea, Brit. Moll. i. p. 366, pi. 23. f. 2. M. glauca, Angloruin. This splendid shell is not British. We have the authority of the French oystermen who bring cargoes of oysters into the port of Exmouth, to plant in the parks, on the Exe, at Lympstone, that it does not even inhabit the Guernsey or Jersey grounds, and that it is a French littoral or laminarian species, and only taken on the in-shore oyster-beds. We have often procured it, the Pileopsis hungaricus, Calyptr&a sinensis, and large Guernsey Chitons, by overhauling the cargoes. Dead valves have been taken on our coasts, either cast thereon by storms or from discharged ballast, a fertile source of spurious species. Near thirty years since, Miss Pococke, daughter of Admiral Pococke, the original assigned authority for this species as British) in person, at Bath, presented the author with two pair of the M. helvacea, taken by herself on the extensive sandy districts of Cornwall ; but she by no means guaranteed their being indigena, and with perfect frankness stated every particular of their acquirement, which scarcely admitted a doubt of their being aliens to Britain. CYPRINHXE. This family consists of four genera, Cyprina, Isocardia, Circe, and Astarte ; the first three have only one species in each, and Astarte six or seven. We have described Cyprina, Isocardia, and Astarte. With respect to Circe, it has not occurred to us alive ; but in the essentials of family configura- tion, of there being no cicatrix in the pallial impression, showing that the tubes or orifices are short or sessile, it agrees with its congeners. It is remarkable that the coasts of Devon give name to the Astarte Damnoniensis, yet, in the forty years we have dredged those localities, neither a living nor 108 CYPRINID.E. dead specimen of that species has been taken; but we have often seen the minute A. triangularis alive. Cyprina and Isocardia by their hinges indicate some alliance with the CardiadtB. This family has considerable affinities with the Veneridce, but is distinguished by the very short, almost sessile siphons, and the consequent absence of pallial impression so con- spicuous in that group. CYPRINA, Lamarck. C. ISLANDICA, Linnaeus. C.Islandica, Brit. Moll. i. p. 441, pi. 29; (animal) pi. M. f. 4. Animal suborbicidar, thick, bluish-white; mantle open, powdered for some depth, on a pale yellow ground, with minute red-brown sandy points ; its edge is finely dentated and marked with a slender brown line. The foot is thick at the base, moderately long, liiiguiform, and posteally lanceolate. The mantle forms no tubes, but mere sessile orifices, both of which are ciliated ; the branchial is the largest, having about twenty simple cirrhi, the anal about ten ; both are tinged with red-brown ; the anal orifice at its terminus frequently pro- trudes a globular transparent membranous valve, which regu- lates the entry and issue of the water ; the margins of both orifices at the base of the cirrhi have a girdle of a narrow bright red line, the hues of which vary in individuals even from the same locality. v This species usually inhabits the littoral sandy districts, but at Exmouth is obtained in an offing of five or six miles. ISOCARDIA, Lamarck. I. COR, Limiseus et Auct. /. cor, Brit. Moll. i. p. 472, pi. 34. f. 2; (animal) pi. N. f. 6. " Animal globular ; mantle completely lining the shell, double at the outer edge; exterior fold divided in front, open TSOCAEDIA. 109 at each end; at the posterior extremity forming two short siphons or tubes, ciliated at the orifices ; colour yellowish- white ; margin orange. Foot very muscular, broad, trian- gular, compressed, pointed, orange. Branchiae external, con- cealed between the mantle and the body. Body soft, com- pletely included within the valves. On being placed in a vessel of sea-water the valves of the shell gradually opened ; the feelers or ciliated fringe of the upper orifice moved slowly, as if in search of animalcules . Having remained in this situa- tion about ten minutes, water was ejected with considerable force from the lower orifice, which till now had remained motionless. The expulsion of the water appeared to be effected by a sudden contraction of the muscles, because this was never done without the valves closing at the same instant. After a few seconds the valves gradually returned to their open position, and remained quiescent as before till the water was again ejected with a jerk. This alternating process was repeated at unequal intervals during the whole time my spe- cimens were under examination, but at shorter intervals on receiving fresh supplies of sea- water, when I suppose the food, the quality of which I could not ascertain, was more abundant. The animal appears to be insensible both to sound and light, as the presence or absence of either did not at all interrupt its movements, but its sense of feeling appeared to be very delicate ; minute substances dropped into the orifice of the mantle instantly excited the animal, and a column of water, strongly directed, expelled them from the shell. With so much strength Avas the water in some instances ejected, that it rose above the surface of three inches of superincumbent fluid. Animal small in proportion to the shell, occupying, when dead, barely a third of the space enclosed in the valves. The mantle is slightly attached to the shell and to the epidermis at the margin, and appears to be kept distended, and in contact with the interior of the valves, by the included water. The valves fit so closely that the animal can remain two days or more without permitting a single drop of fluid to escape. Loco- motion very confined. It is capable, with the assistance of its foot, which it uses in the same manner, but in a much 110 CYPEINID^E. more limited degree, as the Cardiacete, of fixing itself firmly in the sand, generally choosing to have the umbones covered by it, and the orifices of the tubes of the mantle perpendicular. Resting in this position on the margin of a sand-bank, of which the surrounding soil is mud, at too great a depth to be disturbed by storms, the Isocardia of our Irish Sea patiently collects its food from the surrounding element, assisted in its choice by the current it is capable of creating by the alternate opening and closing of the valves." I have been tempted to copy the Rev. James Bulwer's account of this animal from the second volume of the ' Zoolo- gical Magazine/ rather than refer to it, as it singularly corro- borates my views of the mode in which the branchiae of bivalves are supplied with water. That gentleman, after many days' examination, expressly states that the ingress current of water was effected by the opening of the valves, and which was expelled by their closure at the branchial orifice. This state- ment negatives the doctrine of branchial currents by cilia, and ingress and egress currents by separate apertures, that is, by the water being received by the branchial siphon or orifice and discharged from the anal one; besides, this result is anatomically impossible, as all my experiments at least in the closed-mantle bivalves with elongated siphons appear to prove that there is no communication between the anal and branchial tiibes. In this species, the mantle being open, the branchiae receive the water from the great ventral range, and it is expelled by the same channel. We are of opinion that the branchial cilia, the motive agent of the water with many authors, have no other function than to divide it, to facilitate the extraction of the vital influence. "We strongly recommend those naturalists who advocate the doctrine of branchial currents by cilia and distinct siphons or apertures, carefully to consider Mr. Bulwer's account, who at any rate must be looked on as a disinterested observer, and has no object in supporting a particular theory. This genus is artificial, and originates in the shape of the shell ; the animal is so similar to that of Cyprina, that Iso- cardia might very well merge in it. CIRCE. ASTARTE. ill CIRCE, Schumacher. C. MINIMA, Montagu. C. minima, Brit. Moll. i. p. 446, pi. 26. f. 4, 5, 6, 8 ; and (animal) pi. M. f. 3. The animal has not occurred to iis alive. ASTARTE, Sowerby. A. SULCATA, Da Costa. A. sulcata, Brit. Moll. i. p. 452, pi. 30. f. 6; and (animal) pi. M. f. 5. and iv. p. 254, pi. 30. f. 5, 6, and pi. 133. f. 4. A. elliptica, Brit. Moll. i. p. 459, pi. 30. f. 8. Venus scotica and Damnonia, Mout. et Auct. The animal has not been found on the Devon coast. A. ARCTICA, Gray. A. arctica, Brit. Moll. i. p. 461, pi. 30. f. 7- Animal unknown. ? British. A. CREBRICOSTATA, Forbes. A. crebricostata, Brit. Moll. i. p. 456, pi. 30. f. 9. Animal unknown. ? British. A. COMPRESSA, Montagu. A. compressa, Brit. Moll. i. p. 464, pi. 30. f. 1, 2, 3. Venus compressa, Mont, et Auct. This very common Scotch species has not occurred alive. Of the above, the A. arctica and A. crebricostata are very doubtful indigena. A. TRIANGULARIS, Montagu. A. triangularis, Brit. Moll. i. p. 467, pi. 30. f. 4. A. minutissima, Auctorum. Animal occupying a subtriangular yellow or brown strong- smooth shell, crenated at its edges when adult, plain when 112 VENERID^E. young, in which state it forms the A. minutissima of authors. The general colour of the animal is white; the mantle is largely open, with plain margins. There are no siphons ; the anal orifice is sessile. I am unable to say if there is a distinct aperture for branchial functions. The mantle may be entirely open to the anal conduit, receiving the water throughout the ventral range. The foot is finger-shaped, and when much exserted a posterior geniculation is seen ; it is hyaline, mixed with snow-Avhite flakes. No other organs could be seen ; in- deed its minuteness will not allow of any remarks on the branchial structure. The animal was lively, and on the march turned from one side to the other. Taken in the coralline zone at Exmouth, 1852. VEKEBID.E. This beautiful and numerous family, if we take into account the exotic species, is, as regards the British indigena, confined to very moderate dimensions, and in our method only includes the two genera, Venus and Pullastra. With our views of the unnecessary and artificial extension, by the moderns, of many of the Linnaean genera, with scarcely a trace of difference of essential animal organization to support them, for surely a tooth more or less is not an essential point, we entirely concur with M. Deshayes in merging Cytherea in Venus. We examined, about twenty years ago, at Exmouth, a full-grown live specimen of the Cytherean type, the Venus Chione, but we can offer few remarks on its specialties, as, unfortunately, notes were not made on it ; at present we only observe, that it is as decidedly a typical Venus in every essential point as any of the race. We have also no hesitation in consigning the Artemis of authors as a section of the Veneres, though it is said that the foot and coalition of the siphoiial tubes vary from Venus ; but having repeatedly seen the V. exoleta, the type, alive, we can state, that its organs are of the same con- figuration. The V. lincta has not been met with, and is the VENERIDJE. 113 only other British species that has been handed over to Artemis. The genus Pullastra of Sowerby is maintained, though M. Deshayes says that the differences between it and Venus are still less than in Cytherea. We do not concur in this opinion, as that eminent naturalist has overlooked the byssal groove, which essential character, with the general aspect of the group, throwing in as a make-weight the slenderness and parallelism of the teeth, have determined us to adopt it as sufficiently well based on organization. The animals of this family are so extremely similar, that we call in aid their shell-specialties to assist in constituting sections, to facilitate a divisional arrangement for easy identi- fication. The first section comprises the typical Veneres, which have three strong teeth in each valve ; the second sec- tion contains those with four teeth in one valve and three in the other, with a hollow or pit as the receptacle of the isolated tooth ; these are those which authors have deposited in Cy- therea and Artemis. The hard parts of all the species are of very strong and compact texture; their shape is either orbicular tumid and lentiform, or a more or less elongated oval; all have deep siphonal cicatrices, and none have lateral teeth, unless the isolated one of the second section be considered a vestige of one. The animal of Venus has no byssal groove, but I be- lieve that of Pullastra has always that appendage. But these remarks need not be extended, as it will be seen by the specialty descriptions that there are few peculiarities in this old aristocratic family, in which there is little more to do than to ring the changes on trivial points. As I have mentioned the terms Veneridte and Cytherea, and in another place the genera Solenicurtus and Venerirupis, it may not be improper to make a few remarks on the incor- rect Latinization of nomenclatural appellations. This essen- tial appendage of natural history is admitted by all not to be in a satisfactory position, and I will not go beyond the present pages to demonstrate the truth of these opinions. It is the custom of authors to write Venerupis for Venerirupis, Sole- 1 14 VENERID.E. curtus for Solenicurtus. The first may signify a vein of the rock, and the second some connection with the sole of the shoe, or with the Sun, from /So/, solis ; but there can be no mistake in the correct readings Venerirupis and Solenicurtus, which emphatically declare, the one, to be a rock Venus, and the other, allied to the animal of the Solenes. It may per- haps be said, that these are very unnecessary objections ; every one knows what is meant. But that is not a sound reason for writing incorrectly, when it is as easy, without being too fastidious, to have some regard to a just etymology. We may add, that if Venerupis is correct, to be consistent, it would be necessary for the family of the Veneridae to be written Venida. It is the continual neglect of these apparent minutiae that has brought our nomenclature to its present degraded condition. We think, if these points are properly considered, they will be admitted to be essential. These observations are not strictly my own ; I may say, non meus hie sermo ; but I have for them the high authority of a valued friend, now no more, Dr. Goodall, the late Provost of Eton, whose dicta on philo- logy few will dispute, and with whom I have had frequent conversations on the corrupt position of the nomenclature of all the branches of natural history. That learned gentleman, from his profound classical ear, was particularly sensitive on these points and mispronunciations. I well recollect, when chatting together at my house, I pronounced the genus Cythe- rea with the accent on the second syllable, when with offended ear he thundered forth Parce metii, Cytherea ; manent immota tuorum. And yet, with those who ought to know better, we continually hear the word spoken with the accent on the second syllable, instead of the penultimate. I am aware, when the island Cythera is in question, the accent is long on the second syllable alta Cythera, but never in Cytherea. The reproof I received has made a permanent impression, and I have endeavoured to avoid similar error. My object in relating this anecdote is to excite the VENUS. 115 attention of naturalists to the important consideration of nomenclature, and to prevent, at least, additional error, if it be impossible to rectify the present barbarisms. Section I. Three strong teeth in each valve. VENUS, Linnseus. V. FASCIATA, Donovan. V.fasciata, Brit. Moll. i. p. 415, pi. 23. f. 3, and pi. 26. f. 7 ; (ani- mal) pi. L. f. 7. Animal compressed, body flake- white ; mantle open, thick and muscular, bordered with fine white fringe. The siphons are very short, soldered on each other, just separate at their extremities ; the anal is the smaller, slightly curving upwards, furnished with a flexible hyaline valve, and fringed at the orifice with about fifteen plain white cirrhi ; the branchial has twenty rays of similar cast ; both the tubes are of a pale sulphur-yellow, with flaky markings and margined with a fine red line, and are aspersed from their bases with minute sand-like red points. On each side there are a pair of pale brown suboval branchiae, the upper being much the smaller and strongly striated on both surfaces ; the palpi are small, pointed and triangular, externally smooth, but striated across the inner surface. The foot, at rest, is securiform, apparently scarcely detached from the body ; when extended but it is rarely seen so it is thick, moderately long, and lanceolate. The colour pure white. Common, alive, in the coralline zone at Exmouth. V. STRIATULA, Donovan. V. striatula, Brit. Moll. i. p. 408, pi. 23. f. 4, and pi. 24. f. 4, and pl.26. f.9, 10, 11. Animal white ; mantle open throughout the ventral range, having the margin fringed with short fine white filaments. The siphons are rather slender, and when extended are about 116 VENEEID.E. half the length of the shell ; they are of equal length, and united to their extremities ; both have fine red-brown cirrhi at their orifices, which, when the tubes are not fully protruded, are retracted, and give them at that point a naked or truncate aspect ; a good lens is required to detect the cirrhi in this small species. The siphons are pale bistre, and sprinkled with minute red-brown points. The foot is pure white, thickish, and when in action of the usual tongue-shaped sublanceolate form, and slightly angulated at the heel. A pair on each side of suboval pale brown branchiae, and of still paler palpar appendages are fixed in the usual position ; the upper laminae are smaller, of less depth than the under, and more coarsely striated ; the palpi are of the usual triangular form, striated more distinctly on the inner than on the external sides. Common, alive, at Exmouth in all districts. V. OVATA, Pennant. V. ovata, Brit. Moll. i. p. 419, pi. 24. f. 2, and pi. 26. f. 1 ; (animal) pi. L. f. 6. Animal suboval, pale bluish-white, the body being of a deeper flake-white ; mantle open, with the margin fringed with simple thick-set short white filaments. The siphonal tubes in a full-grown animal are rarely exserted more than |ths of an inch, of the same length and united, each with about twenty pale yellow cirrhi, that is, ten long and ten alternate shorter ones ; the orifice of each siphon appears encircled with a fine line, in consequence of each cirrhus having a minute point of that colour at its base ; the anal tube has the hyaline valve. There are on each side of the body a pair of very oblique pale yellow suboval branchiae ; the upper, as usual in this tribe, much the smaller ; they are more striated on the inner than outer surface; the palpi are short, small, triangular, and striated as the branchiae. Foot snow-white, very long, thick, almost cylindrical, and capable of great extension posteally and anteally. The present species is common, alive, at Exmouth. The V. pallida of Turton is exotic. VENUS. 117 V. VERRUCOSA, Linnseus. V. verrucosa, Brit. Moll. i. p. 401, pi. 24. f. 3. We have seen the animal alive at Exmouth, but have mislaid our notes. V. CASINA, Linnseus. V. casina, Brit. Moll. i. p. 405, pi. 24. f. 1, 5, 6. We have not seen this species. Section II. Four teeth in one valve and three in the other, with a pit to receive the isolated one. V. CHIONE, Linn, et nobis. Cytherea Chione, Lamarck et nonnull. , Brit. Moll. i. p. 396, pi. 27. and (animal) pi. L. f. 8. We can at present only refer to our preliminary remarks, and state, that this species will not be found to differ from our Veueridan descriptions, except in minor points. V. EXOLETA, Linn, et nobis. Artemis exoleta, Poli et nonnull. -, Brit. Moll. i. p. 428, pi. 28. f. 3, 4. Shell suborbicular, very convexly lentiform, having the striae of increase close-set, concentric, flattened, slightly re- flexed, and under a powerful lens finely striated in a vertical direction, the surface being often marked with pencils of red, bistre, and dark purple, which radiate from the beaks to the ventral range; some specimens are milk-white, and others with irregular blotches, which sometimes simulate a sort of Arabic characters. There are three teeth in the left valve and four in the other. The margins of the shell are smooth. Animal. General colour pale yellow-white; mantle open from the anterior depression to the siphons ; the margins are fringed with close white cilia, which are most distinct anteally, but as they approach the posterior end become less pronounced, and are resolved into dentations. The siphons are short, scarcely protruding beyond the shell; some authors say,, " siphonal tubes long." We think this is an error ; they arc 118 VENERID^E. united, of much the same size, rufous around the orifices ; the upper almost plain or with a few scalloped points ; the branchial has eight short dull rufous cirrhi. The foot is very large, occupying nearly the ventral range, and always presents itself as of a securiform figure; the heel is rather slender and bluntly pointed, but the rest of the foot can sufficiently pro- tract itself to represent a thick, short, strong, broad lingui- forni organ ; its pure white colour is relieved by beautiful vertical lines of brilliant snow-white. There are a pair of pale brown gill-plates on each side of what are called suboval figures, which in this case stand thus : the dorsal attachment is linear, the free edge curved, expanding posteally in a rounded form, and attenuating as it approaches the buccal orifice ; the upper lamina does not cover the under one ; both show a mixture of coarse and fine strire, the larger being pro- bably the inter -branchial tubes, and the smaller the parallelo- grammic meshes. On each side there are a pair of short tri- angular palpi, strongly striated transversely within, and less so on the outward surface. The liver is brownish-green. The animal is shy and apathetic ; the locomotion consists in screwing the shell on its axis, and turning it from one side to the other. In the coral zone at Exmouth. V. LINCTA, Pulteney et nobis. Artemis lincta, Poli et aliorum. , Brit. Moll. i. p. 431, pi. 28. f. 5, 6. This species has not occurred alive, but fresh shells are frequently taken with the last species. PULLASTRA, Sowerby. P. PULLASTRA, noniiull. et nobis, Venus puliastra, Auctorum. V.perforans, Auctorum. Tapes puliastra, Brit. Moll. i. p. 382, pi. 25. f. 2, 3 ; (animal) pi. L. f. 5 & 5 a. Animal thick, oblong, of the palest bluish-white; mantle PULLASTEA. 119 open, having the anteal and posteal portions of the margin dentated, the middle is smooth and gently sinuated. The siphons, when extended, are fully as long as the shell, and united to about ^ of an inch from their extremities, when they become well separated, the anal one curving upwards, the branchial inclining downwards ; the former is circled with 20-30 pale brown short cilia, sometimes tipped with white, the latter with a variable number of longer brown or pale red ones, each being fringed on both sides with short horizontal white fimbrise; there are also 16-30 shorter intermediates, some plain white, some brown and fimbriated on both margins; the siphons are white, except a short area at their termi- nations below the cilia, of red-brown dark bistre, or of those colours mixed, and marked with short fine red transverse lines and longitudinal blotched ones. A pair of pale brown branchise on each side; the upper laminse not covering the lower, decussated on both surfaces by the network of the blood-vessels; the palpi are small, triangular, striated on the inner surface, and smooth without ; the posterior ends of the branchiae are permanently fixed in this species and the P. de- cussata to the roof of the branchial tube, as in Pholas. The Venus perforans of authors is only a dirty -white or ochraceous specimen of this species, arising from the exclusion of light, in consequence of its habitat being adventitiously cast on rocks, where, like the Saxicavce and other excavators, it has the power of imbedding itself. We have carefully ex- amined and compared with them many of the free shells from the shingles, and have not detected the slightest specific difference : we consider the two identical. The foot of this species is pure milk-white, with a byssal groove producing fine filaments, which, when the animal is not in pure sand, attach it to the shingle ; it is muscular, slightly geniculated, and lanceolate. This is strictly a littoral species, never being met with in the dredge, and is scarce on the shingle tracts at Exmouth. The variety, the V. perforans of authors, is abundant, being imbedded with the Pholas dactylus in the red sandstone at the same place. 120 VENEKID.E. P. DECUSSATA, Linn, et nobis. Venus decussatu, Auctorum. Tapes decussata, Brit. Moll. i. p. 3/9, pi. 25. f. 1. Animal thick, suboval, very pale creamy-white ; mantle open, with the margins finely scalloped or dentated. Foot large, muscular, angulated, lanceolate, white, with a byssal groove. Tubes subcylindrical, gently tapering, separate from their bases, of the same length, and, when extended, as long as the transverse measure of the shell ; they are at times greatly inflated ; the colour, to within a quarter of an inch of the orifices, is pale yellowish-white, interspersed with whiter minute flakes, and marked for about an inch at their termi- nations with confused yellowish-tawny or dark brown short lines or blotches ; both the orifices are fringed, the branchial with about twelve long cirrhi with alternate smaller ones ; the anal has 16-20 of the same size, and generally both are of a bistre colour; the siphons, at the animal's will, diverge in various directions. There are a pair of suboval branchiae on each side, the upper the smaller; they are more strongly pectinated on the inner than on their external areas, of a pale brown, aspersed with minute dark brown points. The palpi are very small for the size of the animal, triangular and striated as the branchial laminae. This species is much more common than the P. puHastra ; they live together in the same shingles, and have precisely the same habitudes; notwithstanding this community they are very distinct species. P. VIRGINEA, Linn, et nobis. Tapes virginea, Brit. Moll. i. p. 388, pi. 25. f. 4, fi. aurea, Brit. Moll. i. p. 392, pi. 25. f. 5. Venus Sarniensis, cenea, nitens, Turt. et Auctoruin. Animal inhabiting a suboval shell, furnished with close-set, blunt, rounded, stout, subconcentric striae ; the ground colour is pale yellowish-white ; the mantle is open throughout the ventral range, with its margins anteally dentated, medially sinuated, and posteally crcnulated, with a few short yellow filaments at each extremity ; the animal emits anteriorly the PULL ASTRA. 121 usual thick fleshy linguiform foot, very moderately geniculated, and capable of all the phases from obtuse to pointed; it is pure white,, and has not the byssal groove of the tribe, which is a considerable variation of structure, and the teeth are not so slender, long, or parallel, more resembling those of Venus, from which this animal scarcely differs. The mantle pos- teriorly forms the siphons, which are soldered together three parts of their length, becoming separated for the remaining portion ; the colour is delicate pale lemon, tinged with red- brown at the bifurcation ; they are of the same size, the branchial being truncate at the extremity, and clothed with fourteen pointed cirrhi, whereof seven are rather the largest, marked at their bases on each side with a patch of bistre, the interstitial ones are white ; the anal tube curves upwards as in its congeners, and does not appear truncate, in consequence of its edges being a little inflexed ; it has sixteen short white cirrhi at the orifice, which has also around it a dirty red-brown fine line ; the tubes, when frilly extended, are less long than in the two preceding species ; they do not, as in Venus, measure more than half the transverse measure of the shell. The pair of subcircular branchiae on each side are pale drab, hung very obliquely; the under ones are at least double the size of the upper, and strongly marked by the transverse vessels of the circulation; the palpi are subtriangular, short, and well striated. The liver appears scanty and of a pale green. This species inhabits the coralline zone at Exmouth, but is rarely taken alive ; dead shells in good condition are frequent. We almost think that this species and its variety the P. Sar- niensis should, from the absence of the byssal groove and the greater divergence of the teeth from the type, be transferred to the Veneres. The P. aurea has not occurred alive ; is it distinct from the present species ? the teeth of the two are of similar character, and if it is without the byssal groove, it would appear that it ought to accompany the P. viryinea to the typical Veneres. 122 DONACID^E. If this family had only consisted of the genus Donax, we would have united it to the Tellinidce; but as it is conjoined to Ervilia, a more aberrant genus, we adopt it. The siphons appear to be shorter than in the Tellinidae, and their cilia of a more complicated structiire ; the dentition is also less simple. There are only three undoubted British species, two in Donax, D. anatinus and D. politus the D. trunculus is probably exotic and one in Ervilia, the E. castanea. DONAX, Linnseus. D. ANATINUS, Lamarck. D. anatinus, Brit. Moll. i. p. 332, pi. 21. f. 4, 5, 6 ; (animal) pi. K. f. 7- Animal elongated, of a purplish- red or yellow ; mantle open on the ventral range, with double margins, the one short, with sinuated or scalloped edges ; the other and outer is clothed with three rows of fringe, the two inner being two sizes of nioniliform white beads ; the outermost or third row has short, close-set, fine filaments of similar colour, altogether presenting a very elegant appearance. The siphons are of the same length, and, when fully exserted, are not more than half an inch; they do not put on a cylindrical aspect, but appear laterally compressed ; they are separate from the bases, and taper gradually to their terminations, which are bordered with very pale orange colour ; the anal siphon is rather the smallest, and furnished with about six white cirrhi; the branchial has 8-10 longer ones, which are fimbriated at the sides, besides plain ones interspersed; when the cirrhi are withdrawn, the terminations of the tubes have a truncate and naked aspect ; a good lens must be used to see their minute developments. The foot is yellow or orange, especially when the animal has been immersed in hot water, very large, flat, bevelled to a sharp edge and lanceolate point when fully DON AX. ERVILIA. 123 extended, but at rest, or half exserted, it is puckered and transversely ridged. There are a pair of light brown suboval branchiae on each side, the upper ones being less and shorter than the lower, hung more obliquely, and scarcely visibly pectinated on either side ; the palpi are rather long, triangular, pale yellow, smooth exteriorly, and well striated on the inner areas. The liver is a pale brown-green. The stylet and attritor are well developed. The ovarium varies in colour from white or yellow to bright red ; it is anterior and under the liver. The rectum, after a convolution or two, passes through the dorsal region, embraced by the heart and white linear auricles, to the anal tube. These beautiful shells are plentifully found with the live animal at Exmouth, and in the littoral and laminarian zones of the Warren sands, between that place and Dawlish. We have not met with the D. politus alive or dead on the western coasts ; we refer to it D. POLITUS, Poli. D. politus, Brit. Moll. i. p. 336, pi. 21. f. 7. D. complanatus, Auctorum. ERVILIA, Turton. E. CASTANEA, Montagu. J5. castanea, Brit. Moll. i. p. 341, pi. 31. f. 5, 6. All that can be said of this animal is, that it has not been observed, though we believe it has been taken alive on the Irish coasts by Mr. Barlee, who favoured us with a small fresh specimen. We trust that indefatigable naturalist will, in an excursion he contemplates again to explore the sea-beds of the Emerald Isle, make us acquainted with the external organs of this interesting species. TELLINID.E. The British Tellinidce are distributed in four genera, Tellina, Scrobicularia, Syndosmya, and Lucinopsis ; their 124 TELLINID.E. shells are, with few exceptions, thin, delicate, of small size, generally having the transverse measure double that of the vertical ; the siphons of the animal are slender, usually sepa- rated to their bases, nearly as proportionately long as in the Pholades, and sparingly cirrhated at their terminations. We consider the posterior flexure of the shell of little distinctive value : all bivalves have it more or less. The most curious incident attached to some of the Tellmidan genera is, the amalgamation of each pair of branchiae into one large lamina, the upper plate being as it were thrown back and perma- nently fixed to the dorsal range, as in the Anatincs a com- munity of structure showing a close alliance between the two families. The genera and species of this group exhibit a greater departure from what are considered the typical points of configuration, than in most others; for example, the external and internal ligament and cartilage march together, as well as the double and single branchiae ; but, notwith- standing the discrepancies of structure, these aberrant genera and species have so much of the family character that they cannot well be placed elsewhere. It may hereafter be necessary to recast the Tellinidcs, and constitute some new families and genera ; for the present, we shall distribute the different groups into sections embracing their aberrations and peculiarities in respect to the typical configuration, but we still hope to supply some useful rectifications. The animals of Tellina and Psammobia are all but identical; a rigorous examination of both does not allow us to state an essential difference either in the internal or external organs ; their shells also scarcely vary ; the posterior flexure in Psam- mobia is almost as apparent as in Tellina. We think the genus might have been dispensed with ; it is probably retained by authors because it forms a break in a long list, if the exotics are included ; but that is not a sound reason for constituting two genera without a difference. We think that an essential service is done to science in relieving it of an artificial genus ; therefore, in our method, Psammobia is merged in Tellina, which forms the first or typical section. As to the supposed difference in the lateral dentition of Tellina and Psammobia, TELLINA. 125 it is of little value, if it even existed, compared with the over- whelming similitude of the entire soft parts, habitudes and habitats of the animals; and we may observe, that in the so-called Psammobia, distinct lateral teeth are often present as well as absent ; the same may be said of Tellina, but in both there are almost always obsolete traces of such laminae. The next section is a small tribe, which, with the external ligament and ordinary dentition of the Tellince, have only one large amalgamated branchial lamina on each side. Lucinopsis next follows, which we have shown to be nearly a strict Tellina. And lastly, Syndosmya and Scrobicularia, furnished with a ligament, that is, both external and internal, besides a spoon-shaped cavity for an internal cartilage, complete the Tellinidan category; these may hereafter constitute two distinct families, as the former has double branchiae and the latter only one large lamina, as in the 2nd section, but cannot be placed in it on account of the very different hinge. These are the most aberrant of the Tellinidce, and immediately con- nect this group with the Anatinidee. The genus Diodonta of Deshayes has been introduced into the British list to receive the Tellina fragilis of Linnaeus and authors. It seems a very useless and artificial one, based on the teeth, and has no new characteristic that differs from Tellina at least we can discover none. We dispense with the genus in its present form, and deposit its only species in the 2nd section of this family. TELLINA, Linnaeus. Section I. The typical species. T. DONACINA, Linnaeus. T. donacina, Brit. Moll. i. p. 292, pi. 20. f. 3, 4 ; (animal) pi. K. f. 4. T. pygmeea, Brit. Moll. i. p. 295, pi. 19. f. 6, 7. Animal oblong, compressed; mantle largely open, not fringed, but finely dentated. Siphonal tubes long, separate from their bases, plain and simple. Foot pure white, flat, broad, long, and lanceolate. On each side of the body there are a pair of pale brown suboval branchiae, nearly of the same 126 TELLINULE. size, smooth on the outer surfaces, and on the inner striated with about thirty of the delicate vessels of the branchial circu- lation ; the corresponding pair's of subtriangular palpi are also pale brown, smooth on the outside, except showing a longi- tudinal furrow, and pectinated within. These beautiful shells are frequently taken alive in the coralline zone at Exmouth. This animal may be placed, par excellence, at the head of the typical species. T. CRASSA, Montagu. T. crassa, Brit. Moll. i. p. 288, pi. 20. f. 1, 2. Animal suborbicular, lentiform ; the general ground colour is pale drab; mantle quite open, double-edged, finely, closely and conspicuously fringed, produced posteriorly into two long rather slender siphons, separate from their bases, the branchial quite plain at its termination ; the upper or anal one, which is apparently rather the largest in diameter, and capable of great inflation, has six triangular points at the orifice ; their ground colour is marked with two or tliree intenser whitish longitudinal lines. I am unable to state how far the tubes can be extended, as the animal was sent to Bath in 1851, wrapped in moist sea- weed, accompanied by bottles of sea- water, and had become partially collapsed; but I should think, judging from other Tellina, that in the specimen exa- mined they would, when fully exserted, be at least 2 inches long. The shell was the largest I had ever seen, measuring transversely 2|, and vertically 2g inches. The foot is the usual large, spatulate, thick, muscular, linguiform appendage of the TeUina, perfectly simple, without a trace of a groove in the heel. The pair of branchiae on each side are subcircular, of very thin texture, the lower of great extent, the upper not half the depth of its larger fellow ; both coarsely but not distinctly pectinated. The palpi, a pair on each side, are nar- row, slender, pointed, of a very elongated triangular shape, quite smooth externally, but well striated within. The liver is anterior, of a dark brownish-green ; the stomach contained the usual tricuspid membrane, or attritor, and the crystalline stylet of large size. The heart, auricles, nervous ganglia, with TELLINA. 127 the stomach and intestine, exhibited no peculiarity. The large posterior dorsal mucous gland was well developed, the colour being a moderately dark brown : this gland crosses the dorsal line near the posterior adductor, and perhaps is a receptacle for the pigments of the mantle. This species inhabits the coralline zone at Exmouth, but is rarely taken alive of good size. T. FERROENSIS, Chemnitz et nobis. Psa mmobia farroensis, Brit. Moll. i. p. 274, pi. 19. f. 3. Animal elongated, compressed, white or of the palest brown ; mantle open, with the margin clothed with a short white fringe, or rather fine dentations. The siphonal apparatus con- sists of the usual slender separated tubes, the branchial being rather the longest and largest, having six plain cirrhi at the orifice ; when not fully extended it appears finely corrugated, and has two longitudinal bars on the surface ; the anal siphon curves upwards, the orifice being destitute of cirrhi. The foot is very large, flat, long, bevelled to a sharp edge, and lanceo- late. There are a pair of branchiae and a pair of palpi on each side ; the under laminse are by far the largest, long, deep, and subquadrangular ; the upper ones are not above half the size, of suboval shape, and have a lanceolate ter- mination, hanging on the posterior portion of the large ones ; they are all visibly striated on both surfaces; the palpi are long, subtriangular, and very well pectinated. The liver is pale green, conjoined with the pale yellow ovarium, which in July is full of ova in all states of development. This elegant and variously coloured species as to the shell, is frequently taken in the dredge in the coral zone in a living state. T. TELLINELLA, Psammobia tellinella, Brit. Moll. i. p. 277? pi- 19- f- 4; and (animal) pi. K. f. 1. P. florida, Turton. Animal elongated, compressed, pure white; mantle open, dentated ventrally, and fringed posteriorly from the beaks to 128 TELLTNKLE. the tubes. The siphons are moderately long, disunited, taper- ing and divergent; the anal one is the longest and most slender, curving upwards with exceedingly minute cirrhi at the extremity, of frosted white, and eight intenser longitudinal fine Hues running from base to point ; the branchial siphon is also frosted white, having six short cirrhi at the orifice, and intermediate shorter ones. There are a pair of pale brown suboval branchiae, which hang obliquely; the upper very small, lapping on the much larger lower ones almost verti- cally ; they are on both sides coarsely striated, the larger by only eight vessels of the circulation, separated from each other by as many fine lines. The pairs of palpi are rather long, subtriangular, pointed, pale brown, smooth outwardly, and within coarsely pectinated transversely, not having the furrow as in those of T. donacina. Foot flat, sharp-edged, slightly gemculated, linguiform, lanceolate at the point and pure white. These animals are dredged in abundance at Exmouth, in a six-mile offing. The following species have not been met with alive. T. INCABNATA, Liniiseus. T. incarnata, Brit. Moll. i. p. 298, pi. 20. f. 5. T. BALAUSTINA, LilinffiUS. T. balaustina, Brit. Moll. i. p. 290, pi. 21. f. 2. T. FABULA, GronoAius. T.fabula, Brit. Moll. i. p. 302, pi. 1.9. f. 9. T. PROXIMA, ? Brown. T.proxima, Brit. Moll. i. p. 307, pi. 21. f. 1. T. BRIMACULATA, Linnseus. T. brimaculata, Brit. Moll. i. p. 309. T. VESPERTINA, Chemnitz. Psammobia vespertina, Brit. Moll. i. p. 271, pi. 19. f. 1, 2. T. COSTULATA, Auctorum et nobis. Psammobia costulata, Brit. Moll. i. p. 279, pi. 19. f. 5. We are not certain, though we believe most of the above belong to this section ; but we have doubts on the T.fabula, as the authors of the ' British Mollusca ' observe that its TELLINA. 12i animal is like that of T. tennis, which has only a single amal- gamated branchial lamina on each side, and belongs to our second section ; in that case, the T. f alula must march with it. But this point may easily be set at rest, as the species is common, though not in my district. The T. proximo, is exotic or fossil. The T. bimaculata is exotic. The T. balaustina of British origin has much similarity to specimens of T. crassa of the same size ; the hinge, teeth, cica- trices, and pink radiating pencils are identical ; the chief dif- ference is the greater tumidity and tenuity of the valves, and the absence of the short vertical lines between the striae of increment. Section II. Animal with a single branchia on each side. T. TENUIS, Da Costa. T. tennis, Brit. Moll. i. p. 300, pi. 19, f. 8; and (animal) pi. K. f.3. Animal very flat ; mantle sufficiently open in the ventral range, finely fringed, produced posteriorly into two white siphons, separated from their bases, of about equal length and diameter ; both of them are often exserted beyond the length of the shell ; the anal is usually the longest, and curves up- wards; but these circumstances depend on the will of the animal. There is only one very large pale brown, excessively membranous, subtriangular branchia, on each side, with the finest pectinations, fixed under the posterior dorsal range, where its point becomes united with that of the one on the other side, exactly as in T. solidula, but its margin is not fixed to the body so decidedly ; it is more lax, and can be elevated by a camel's-hair brush, and is connected at the anterior angle by a branchial vein, with a pair on each side of large triangular palpi, but not so much out of size as in T. solidula and Scrobicularia piperata ; they are pectinated on both sides, but more so on the inner surfaces ; the colour is a darkish cloud hue, mixed with paler lines, giving them a mottled aspect ; they are broad at the bases, not very long or pointed. The foot is large, broad, compressed, tongue-shaped, not very pointed, and geniculated. The liver is dark green ; K I'M TELLINID^E. the ovary anterior, running to the lower part of the body, is at this season (July) full of white ova in various stages of maturation. The stylet and stomachal attritor are present ; indeed we believe that they may be found in every bivalve. These notes, with those on T. solidula, suggest the query, ought not the two, and any other of similar branchial struc- ture, to be removed from the typical Tellinte, to a distinct Tellinidan genus ? The singular character of the single com- pound branchial plate on each side, their oblique, almost vertical position, together with the form, disposition and enormous size of the two pair of triangular palpi, so entirely different in the Telling of the first section, would appear to sanction such a procedure. T. SOLIDULA, Pulteney. T. solidula, Brit. Moll. i. p. 304, pi. 20. f. 6. Animal suboval, thick ; mantle of strong and firm texture, tumid at the margins, which have a fine short lead-coloured fringe, closed posteriorly, and forming two very long hyaline siphons ; the anal one turns upward, and is often exserted to almost twice the length of the shell, plain at the orifice ; the branchial is usually less extended, and has 4-6 very minute dentations at the aperture ; in the protrusion of the tubes the animal is very capricious, often exserting the branchial far beyond the anal one and vice versa, which has led authors into descriptive mistakes. The siphons are disunited from their bases. The foot is white, very large, thick and fleshy, of a lanceolate shape, but not very long and pointed, geniculated, and without byssal groove. The branchial apparatus is cu- rious, and a departure from the TelHna type ; it consists of a single rather elongated branchial plate, on each side, situated towards the posterior half of the animal ; it is fixed to the dorsal range by its base running obliquely, indeed almost vertically from the dorsal to the ventral range, becoming joined to its fellow under the posterior and smaller part of the body, by a permanent membrane. The whole area of the plate is well fixed, the two sides being scarcely free at the TELLINA. 131 edges; the branchial artery divides it nearly in two equal parts ; it may be considered as a pair of laminse, which, instead of being folded or falling on each other, as in the ordinary bivalves, are thrown open and permanently fixed to the poste- rior area of the body. The colour is brownish drab, with a yellow or fawn-coloured patch in two or three places ; anteally there are on each side two enormous triangular, broad at their bases, pointed palpi, smooth without and well striated within ; they are so large as nearly to have the aspect of small pairs of branchiae ; they are in connection by one of their angles with the branchial plate, and with each other by labia around the mouth. The colour is drab, aspersed with very minute sand- like, pale red-brown points. The liver is brownish-green and united anteriorly with the ovarium. The elastic stylet and corneous stomach attritor, called by most authors the tricuspid membrane, is particularly firm and conspicuous in this species. It thus appears that our present animal differs greatly from the typical Tellince, in the branchial plate and character of the palpi, and thick obtuse foot. This species has also a rather close alliance with Scrobicu- laria piper at a, which has like it only one compound bronchia on each side. T. FRAGILIS, Linn, et Auctorum. T.fragilis, Philippi, Moll. Siciliae. Diodonta fragilis, Brit. Moll. i. p. 284, pi. 21. f. 3 ; (animal) pi. K. f.2. We are not aware that any British author has observed this species. The following is a translation from M. Phi- lippi' s very insufficient notice of it, in the 'Enum. Moll. Sicilise/ vol. i. p. 28 : "Animal with two siphons, the lower or branchial being nearly double the length of the shell, the upper scarcely so long as the shell; without cirrhi at the orifices ; the foot is small, oblong, lanceolate, with very large oval palpi." We can say nothing of M. Deshayes' description of the animal organs. In the ' British Mollusca ' we have some further particulars : Mantle fimbriated at the edge ; siphons of unequal lengths, separated from the bases, and, contrary to K *> K .- 132 TELLINID.E. Philippi, stated to be cirrhated at their apertures; foot not very large, without byssal groove. Nothing is said in either account of the branchiae, and Philippi only observes that the animal has very "large oval palpi"; from which we hazard an opinion that it may belong to our second section, in which there is only one compound branchial lamina, and excessively large palpi on each side of the body. In these extracts we have a strict description of a true Tellinidan, of either the first or second section. The teeth also are those of a Tellina, either without or with obsolete laterals. Diodonta therefore is only synonymous with a Tellina of one or other of the sections. But if, from the very considerable variation of animal structure in the two divisions, it should be thought advisable to con- stitute a distinct genus for the second section, with the single compound branchia on each side, and Diodonta should realize our conjectures as to a similar form of the organs, it would have priority over any other generic term, and in that case would receive as congeners T. tennis, T. solidula, and perhaps T. fabula. These are the reasons that have induced us provisionally to deposit the T. fragilis in the second section, until we have further information on the required points. And we invite naturalists who are in the vicinity of this interesting species publicly to record their notes. LUCINOPSIS, Forbes and Hanley. The Venus undata of the older conchological authorities, which has been justly separated from Venus by more recent writers under various appellations,, and particularly by the learned authors of the ' British Mollusca ' under the title of Lucinopsis undata, has given rise to much difference of opinion amongst malacologists in regard to its natural position. Though the shell of this species, anomalous in several points, has long been known, the aggregation of the curious charac- ters of its animal has never been sufficiently described, from the difficulty of procuring it alive of large size. The quotation from my manuscript in the ' British Mollusca ' is the result of LUCINOPSIS. 133 the examination of very small specimens, not more than |ths of an inch diameter, though it is as correct and full as could well be expected from such materials ; but the receipt from Exmouth of adult lively examples of If inch diameter, has enabled me to review and add to it several unrecorded features, which I think will interest malacologists, and show that this peculiar genus has scarcely yet received its precise natural allocation; and many important circumstances will be de- veloped, which may assist to determine the proper station of some other bivalve molluscan groups, by the concatenation of characters exhibited by this animal, illustrative of its con- nection with them. L. UNDATA, Pennant. L. undata, Brit. Moll. i. p. 435, pi. 28. f. 1, 2 ; (animal) pi. M. f. 2. Venus undata, Auctorum. Animal inhabiting a shell of thin and fragile texture, like many of the Tellinae, irregularly subrotund, and not exhibiting the decided lenticular form of its shell ; the general colour is pale pinkish-drab, which, when the animal has been killed by hot water, often changes to the various hues of orange, red, and brown : this remark is of some importance as regards correct description, for under similar circumstances this con- dition prevails more or less in all the testaceous Mollusca, and particularly in the bivalves. The mantle has its edges sinuated or furbelowed, in some examples irregularly jagged, but not serrated ; the ventral aperture is very contracted, only affording space for the issue of a moderately sized foot, in consequence of the basal position and very large size of the posterior adductor; and though the anterior one is nearer the dorsal region, it also, from the length, contributes to the smanness of the pedal aperture ; the mantle is produced posteriorly into two very long pale orange siphons, divergent and separated to their bases ; the branchial one is the smallest and longest, being in adult examples in full extension 1| inch long, and having the extremity margined by a circle of very short, minute dark lines, blotches or dots, with 1620 white cirrhi of irregular sizes and lengths ; the anal siphon is of rather 134 TELLINIDJL larger diameter, and when protruded is "barely an inch in length; its extremity is furnished with 12-15 white, short cirrhi, of more uniform length than in the branchial ; it has not the dark terminal margin of points : the usual hyaline valve was not observed, but it probably exists. This siphonal apparatus has the entire aspect of that of the typical Tellinidce ; but its position when exserted is singular, being very little posterior to the centre of the ventral range, instead of being, as is more usual, protruded from a posterior angle somewhat more basal than a right one to a vertical line drawn from the beaks to the ventral centre; this nearly central basal site is occasioned by the great size and low position of the posterior adductor, which necessarily compels the issue I have described. The foot is white, not large, flat, bevelled, pointed, very little geniculated, without a byssal groove, scarcely differing from the Tellitue and some of the Veneres ; it also, from the causes assigned to the siphons, has a more basal position than usual when protruded, with a very limited anterior action, from which it may be inferred that the motive power is con- fined to the turning from side to side and on its centre. The branchiae are subcircular, the upper plates being much less than the lower, half lapping on them, pale drab, with mode- rately fine but not very distinct pectinations ; the pair of palpi on each side are fleshy, rather long, triangular, pointed, strongly pectinated on the outsides, smooth within, and con- nected with each other around the mouth ; they are also light drab. The body is pale pink, small and subglobular, having the foot fixed to its centre. The liver is grass-green. I have already alluded to the texture of the shell, but it is necessary to add, that in the right valve there are two laminar primary teeth, and in the left two similar ones, with a strong double tooth between them : there are no laterals. It would then appear, that the texture of the shell, the two laminar teeth in the right valve, and the exact similitude to the typical Tellince, of the very long, slender, divergent siphonal apparatus having each tube completely separated to the base, allv this animal by many degrees nearer to the TellinidtB than LUCINOPSIS. 135 to the Veneridee, as none of the genera of the latter family have any resemblance to this siphonal condition; still it cannot be lost sight of, that the three primary teeth in the left valve, which appear in no tribe but in that of the Veneres, give it a decided connecting link with them. As to the alliance of Lucinopsis with Lucina, it is not very near, and principally consists in its lenticular shape, which, however, is that of many of the Veneres, so that a less signi- ficant appellation might have been preferable. I must likewise observe, that there are some differences of shape and position from either the Tellince or Veneres in the adductor cicatrices of Lucinopsis, which have a slight approach to the Lucina ; in other respects there is little in common between the two, there being no siphonal apparatus, and a very peculiar foot in Lucina. These remarks may induce malacologists to take into con- sideration, that, the Tellinidce and Veneridee being so closely allied by the intervention of Lucinopsis, it would be desirable to remove Mactra into the vicinity of Cyprina, to precede it and follow Cardium, in which case the line would march thus : Cardiadce, Mactridce, Cyprinidce, the Veneridee, then the Donacidce, the Tellinidce, and their genera, &c. ; and thus, by relieving the Tellinidce and Veneridee of the intermediacy of the Mactrce, perhaps a greater approach to a natural position would be obtained. The peculiar characters of the shell of Mactra create a diffi- culty with respect to natural order, as it has many features of the Myadce and Anatinidce ; but the open mantle of the animal will not allow it to be so near a neighbour to them as to follow the Tellinidce ; neither can it remain between the latter family and the Veneres, the union of which, I think, is more naturally effected by Lucinopsis, notwithstanding the anomalies that exist in that genus. The siphons of Mactra are altogether different from those of the Tellince ; their tubes are more con- gruous with the Veneridee, so that it might have been placed immediately after the typical Veneres if the Cyprinidce had not intervened, which, however, cannot be severed from them, merely because their siphons arc so short as scarcely to pro- 136 TELLINID^E. duce a scar ; therefore it would appear difficult to fix Mactra otherwise than to follow the Cardiudae, and come into line between them and the Cyprinidce. SYNDOSMYA, Recluz, S. ALBA, Wood. S. alba, Brit. Moll. i. p. 316, pi. 17. f- 12, 13, 14. Mactra Boysii, Montagu. Animal suboval, compressed, very pale bluish-white ; mantle open, with the margin dentated. The branchial and anal siphons are separate from the bases, very elastic both laterally and longitudinally ; when in full action cylindrical, and ordinarily as long as the shell, often much longer. The animal can inflate them to three times their usual diameter ; they are light brown, the effect of an epidermis, the ground colour being white; when half exserted they are strongly corrugated. The branchial siphon is truncate and simple at the orifice ; the anal has the usual tubular hyaline valve, and is otherwise plain. The branchiae are a pair on each side, suboval, pale brown, symmetrical, hanging obliquely from the dorsal range; in our small specimens we could not satisfy ourselves on the character of the palpi, but think the large branchife are carried round the mouth without a solution of continuity, as in the Arcadae ; they are well pectinated within and smooth without. The foot is large in proportion to the animal, muscular, slightly angulated at the heel, lanceolate, white, without a byssal groove. The ventral portion of the body is marked with intensely white spots. The liver is green, and the ovarium of a bluish-white colour, full of ova in August. This is an aberrant genus of the Tellinidae ; in the shell and organs of the animal it presents singular departures from what we have been accustomed to consider the typical points of their organic structure. This genus requires a careful exami- nation of its species, which may eventually, in conjunction Avith Scrobicularia, lead to the formation of a family inter- mediate to the TeUinidffi and Anatinidte. At one time we SYNDOSMYA. 137 thought the Scrobicularia piperata should be amalgamated with the Syndosmyte, but a careful review of the two ani- mals in 1849 has convinced us that there are considerable organic variations, particularly in the arrangement of the palpi and in the size of the branchial laminse, which in Syndosmya alba are of equal dimensions, but in S. piperata completely discordant ; again, the habitats of the two are very different, the "piperata " being imbedded for a foot or more in the pure muddy deposits of the estuaries, whilst the Syndosmya live in the mud of the sea-beds of the South Devon coasts, two or three miles from shore, and are taken alive at Exmouth, Dawlish, and Babbacombe Bays. Exmouth, 3rd August, 1850. An examination this day of large specimens, shows that there are a pair on each side of nearly equal suboval branchiae, and a single large palpum, broad at the base, triangular, not sharp-pointed nor very long, and slightly pectinated, divided in the centre by a depressed line, probably the artery; this gives the aspect of two narrow palpi. This plate is connected at its angular point with its fellow on the other side. S. PRISMATICA, Mont, et Auct. S. prismatica, Brit. Moll. i. p. 321, pi. 17. f. 15. Animal compressed, white; mantle open throughout the ventral range, finely fringed, forming a siphonal apparatus of two long, slender, separated tubes, nearly of the same length ; both have 57 short cirrhal points at the orifices, which are sometimes obsolete ; the anal tube is of the lesser diameter, but the animal often greatly inflates it, particularly the ter- minus, into a bulbous or club shape, and then instantly attenuates it to a filiform state as fine as a needle. The tubes, when not withdrawn, are corrugated, and covered with a very thin pale brown epidermis. There are, on each side, a pair of suboval branchial laminse, of equal size, well pecti- nated, and also a pair not a single palpum, as in S. alba, if we are not in error with respect to that species, of thin, short, broad, triangular pointed palpi, smooth without and striated 138 TELLINID^E. within. The foot is long, broad, flat, large, white, pointed, and geniculated, as in Tellina ; indeed, the animal is closely allied to that genus ; the greatest difference is in the shell, which, with the outward ligament of the Tellince, has also a small internal cartilage fixed in an oblique cavity. The liver is dark green, placed at the summit of the dorsal line. We extracted the crystalline stylet and attritor, called by authors the tricuspid membrane. It inhabits, sparingly, the coralline zone at Exmouth. The two following species have not occurred : S. TENUIS, Montagu. S. tennis, Brit. Moll. i. p. 323, pi. 17- f. 11. S. INTERMEDIA? Thompson. S. intermedia! Brit. Moll. i. p. 319, pi. 17- f- 9, 10; (animal) pi. K. f. 5. We very much think that the S. intermedia is nothing more than a variety of S. prismatica, being the result of climate. SCROBICULARIA, Schumacher. S. PIPERATA, Grnelin et Philippi. S. piperata, Brit. Moll. i. p. 326, pi. 15. f. 5 ; (animal) pi. K. f. (J. Mactra compressa, nonnull. Animal suboval, compressed, pale yellowish-brown ; mantle open, with a fringe only visible by the aid of a good lens ; the siphons are nearly as long as the shell, separate from their bases, of the same length, subcylindrical, tapering to the extremities, which are truncate, without cirrhi, of a pale dirty- brown, the effect of a fine epidermis. There is, on each side, a single, subangular, pale yellow branchia, running obliquely, I may say almost vertically, from the dorsal to the ventral range, very finely pectinated on the outside, but more in- tensely within ; the two palpi, on each side, are large, thin, flat, very long, triangular, broad above, pointed at their ter- minations ; they present the same characters as to colour and pectination as the branchiae. This is strictly a littoral species, inhabiting the quiet muddy ANATINIDJE. 139 inlets. At Exmouth they are of very large size, often more than 2 inches transverse measure, of a fine ochraceous colour ; the fishermen call them " mud hens." ANATINID^. This family, according to our views, contains only a single genus, Anatina, long used by authors for this group, but which, without good reason, has been dismembered and split into the genera Lyonsia, Osteodesma, Thracia, Cochleodesma, Periploma, Necera, and Poromya. We have examined more specimens of the four first so-called genera, than are sufficient to entitle us to say, that the animals of all of them are identical as to essentials of the soft parts, and there is also, in all, the great conchological characteristic, the accessorial testaceous ossicle. I believe that the generic term Anatina has the priority, but it is a matter of indifference if either of the other appellations are applied, so that we have not eight genera for the same animal. All this confusion has arisen from M. Deshayes having, in his comments on Lamarck, shown that he had not observed the animals, by having collected and adopted the artificial genera of authors; what is more remarkable, this eminent zoologist admits that he did not know whether all the species of the tribe were provided with the ossicle, and instances as doubtful the A. myalls of Lamarck, our A. de- clivis. We have not only seen the testaceous accessory of this species, but of every other British Anatina; that ap- pendage is the invariable distinguishing character of this family, which is the only one that is furnished with this curious cardinal internal distinct testaceous addition which clasps the valves, or is imbedded in the cartilage of the apophysary cavity ; its shape is various, usually a semilmiar minute cord, sometimes subtrigonal ; it is exceedingly brittle, in appearance at least, except in A. norvegica. We scarcely know its use in the animal ceconomy, but presume it is to fortify the hinge, by acting like the check-tape of a trunk to prevent too great an opening and strain on it. 140 ANATINID^E. We have named Periploma, but are not aware that any British species has been consigned to it : as to Ne&ra and Poromya, newly constituted genera, our reasons for intro- ducing them to this family will appear hereafter. The Anatinidce have some connections with Corbula and Pandora, but the greater length, separation, and slenderness of the siphons still remind us of the vicinity of the TeUinidce. A malacological character of high importance is attached to this group, which we consider decisive of the propriety of merging in Anatina the Lyonsia or Osteodesma, and the Thracia and Cochleodesma of authors, which is,, that all the British members of these genera have only a single branchial lamina on each side. Two or three of the TelHnce have a similar structure, but they are mere exceptions to a rule, and evidence the point of passage between the Anatinae and Tellince ; but in Anatina it is, we believe, the rule ; though we cannot positively assert that it applies to Neasra and Poromya, yet there is little doubt that it does ; but as the species are not uncommon in Scotland, we hope that the Northmen will enlighten us on this point. ANATINA, Lamarck. Thracia, Receutiorum. A. PHASEOLINA, Lamarck et nobis. Thracia phaseolina, Brit. Moll. i. p. 221, pi. 17. f. 5, 6; (animal) pi. H. f.4. Animal subovally elongated, moderately thick, pale brown ; mantle closed, except a fissure quite anteriorly for the passage of a compressed, not very long, spatulate foot, with a rounded extremity, and posteriorly, for the issue of two moderately long siphons, which are separate nearly their length, but the animal always carries them in a divergent posture at the extremities; both are furnished at the orifice with a few minute rays ; the tubes are capable of great inflation. There is only one large, suboval, pale brown branchial lamina on each side, smooth within and pectinated without ; each lamina ANATINA. 141 is divided in two parts by a strong deep oblique furrow by which it is attached, and may be that in which the artery or vein runs; the lower part of each plate is free, and can be raised as far as the furrow ; we may say that the branchiae, instead of being doubled, lay open and present in each the same area in one large plate, as if they were in two. The furrow gives the appearance of two branchise ; but it must not be supposed that the upper portion nearest to the dorsal line has been displaced or thrown back by accident ; it is securely fixed thereto by its membrane, and thus forms a single open plate. This branchial arrangement is confined to very few families; the Anatina constitute its head-quarters; all the species probably have it ; in this we have only detected one short triangular palpum, but there may be two, or the rudi- ment of a second; in A. norvegica, of the same branchial form, there are two complete palpi. The foot is bluish- white, not lanceolate, in the animal now described; but in our notes, written many years ago, it was stated to be lanceo- late, and it may be so : this apparent discrepancy perhaps originates from the present animal having had a part of the valve lacerated, thus preventing the full exsertion of the foot, and giving it a blunt and rather clavate extremity. We pro- pose this species as the type. Live and dead shells are frequently dredged in the coral zone at Exmouth, the latter with rarely the ossicle ; in the live ones great care must be taken not to remove it with the animal. This species, termed Mya pubescens by the older authors, was long considered the young of Pennant's and our A. de- clivis, until, by a suite of specimens dredged by us many years since, we demonstrated that it had true specific pre- tensions. A. INTERMEDIA, nobis. A. villosiuscula, Macgillivray. Thracia villosiuscula, Brit. Moll. i. p. 224, pi. 17. f. 4, 7- Having examined numerous live specimens of this species, it would be a mere repetition of the notes of the type to say 142 more than that it is scarcely distinguishable from it malacolo- gically. The shell is rather more convex, the posterior end shorter, more arcuated and scabrous, not quite so broad, and the ossicle somewhat more wiry than in A. phaseolina : the two when adult are about the same size. I am the original discoverer, more than thirty years ago, and named it specifically intermedia, by which appellation it was long known on the Devon coasts, and in private collec- tions, but I neglected to substantiate my claim by publication. Agreeably to the ' British Mollusca/ i. p. 224, Mr. Macgillivray described and named it Anatina villosiuscula, in Jameson's Edinburgh Philosophical Journal, 1827. Of course by my laches I lost my discovery ; but it is strange that Professor Macgillivray, in his ' Mollusca ' of Scotland, in 1844, passes over his own previous notes and my discovery without the slightest recognition. It is possible the learned Professor may have had reason to doubt the honour of paternity, and thus handsomely consigned it to the care of the " vrai Amphitryon." Consequently, under this view, I feel that I am morally, if not strictly, entitled to take care of my own bairn. A. NORVEGICA, Chemnitz et nobis. Lyonsia norvegica, Brit. Moll. i. p. 214, pi. 8. f. 6-9; (animal) pi. H. f. 3. Mya norvegica, Auctorum. Animal elongated, rather thick, of a pale brown aspect, except the foot; the liver is grass-green. The mantle is closed, leaving only an opening for the foot close to the poste- rior end. The margin of the pedal aperture is strongly scal- loped, marked between the dentations with black points, as well as on the sutural line of the mantle for some distance on both sides of it. The foot is pure white, flat, broad at the base, tapers to a point, and is cloven at the heel, from whence byssal filaments issue. The siphonal processes are two short tubes, which appear enclosed in one sheath, that has the margin finely dentated ; each orifice is garnished with about eight white simple cirrhi and as many black equidistant points at their external edges ; the surfaces of both tubes when ex- ANATINA. 143 serted are sprinkled with minute red-brown points ; the anal siphon is conically pointed, and protrudes the usual hyaline tubular valve ; the branchial is truncate. The branchiae are narrow, elongated, pale brown, and composed of only one lamina, on each side, which have all the incidents of that organ in A. pliaseolina, to which we refer; but there are two distinct palpi, that are long, narrow triangular, pointed, pecti- nated within, and less so 011 the outer surface, of a similar colour as the branchiae. We believe that most of these animals emit byssal filaments. These notes show that this species is in close accordance with its congeners ; the testa- ceous subtriangular ossicle of the hinge emphatically pro- nounces it a member of the Anatinte. The lustrous aspect of the interior of the valves has been considered of greater im- portance than it deserves; that character may indicate an affinity with Pandora, but, as far as regards generic consi- derations, is of little value. Nothing can outweigh the cha- racters of the ossicle and single compound branchial lamina on each side the body ; these indelibly mark the position of the present species. This very elegant object is often taken in the coral zone at Exmouth. In empty shells the ossicle is absent ; but we have at certain seasons captured many live specimens. The sandy coat with which the shell is clothed for the protection of the animal must be removed before all its beauty can be seen. A. CUSPIDATA, nobis. A. brevirostris, Brown. Tellina cuspiduta, Olivi. Necera cuspiduta, Brit. Moll. i. p. 195, pi. 7- f- 4,5,6; (animal) pi. G. f. 4, 5, 6, 7- N. costellata, Brit. Moll. i. p. 199, pi. 7- f. 8, 9 ; (animal) pi. G. f. 8, 9. N. abbreviate^ Brit. Moll. i. p. 201, pi. 7. f- 7- We have no hesitation in relieving the British list from the genus Neeera ; indeed we have no choice, as its only species is a strict Anatina the Thracia of the moderns having the crescent-shaped, or in this case, the double paralleled sub- 144 ANATINKLE. circular ossicle clasping vertically the two valves. This is Hobson's choice ; for we presume that all malacologists are aware that no other genus except Anatina is armed with this singular distinction. There can be no mistake, as we have in our cabinet the ossicles separately displayed, and they prove by their identity that the " costeUata" and "abbreviata" are the scions of the type, the latter being the young, and the former a variety. Many bivalves of the same species differ much more in their varieties ; for example, the strongly punctured, and the nearly smooth Lepton convexum. Brown in the first in- stance placed this genus and species properly as the Anatina brevirostris, but unfortunately, to truckle to the fashionable nomenclature of the day, he changed it to Thracia brevirostra ; but it is probable Olivi's specific title has the priority. For what is known of the animal we refer to the ' British Mollusca/ under the titles Necera cuspidata, N. costellata and N. abbreviata. If the diligence of malacologists had been a little more awakened to the observation of the conspicuous ossicle, they might have spared themselves some trouble by depositing their articles in genera already constituted, and singularly appropriate. This species is taken sufficiently abundant on the Scotch coasts. A. GRANULATA, nobis. Corbula ? granulata, Nyst and Westendorf. Poromya granulata, Brit. Moll. i. p. 204, pi. 9. f. 4, 5, 6. This is the Poromya of authors. To prevent repetition we refer to our general remarks on the Anatina cuspidata. We are almost afraid, that in admitting this species as distinct from Anatina convexa, some error may be committed. We have most carefully examined the hinge of the two, and find it essentially the same ; both have the ossicle and their poste- rior extremities bi-angulated ; they have the same shagreen- like points or punctures in the test, increasing in intensity at the margins; the siphons have the similar short character, and are in like manner ornamented with cirrhi or filaments of different lengths ; both present on each side the broad amal- ANATINA. 145 gamated single branchia, the invariable condition of all the Anatinae ; at least we judge so in respect of the present species from a perfect dried animal, which, when saturated with moisture, appeared to support this view ; and as regards the A. convexa, though we have not seen it alive, we determine by the analogy of several that have been examined. The contour of the two is only slightly different in many young or dwarf examples of the " convexa." In saying this we do not mean to insist on identity. At any rate, enough surely has been stated to convince, that the two are absolutely congeneric, and, if not identical, they are all but so. For an account of the animal of this Scotch production we refer to the ' British Mollusca/ i. p. 204, and iv. p. 250, of the Appendix. A. BIDENTATA, noblS. Montacuta bidentata, Brit. Moll. ii. p. 75, pi. 18. f. 6 & 6 a. We feel sufficiently confident to remove this species from the modern genus Montacuta to Anatina : the distinct con- cave subcircular ossicle, which we can show in specimens, and the bi-angulation of the siphonal extremity - - the invariable characteristic of Anatina left us no alternative ; indeed our observations on Lepton Clarkice must have prepared mala- cologists for this removal. I allude to the mention of the ossicle, which is of such high authority as to require no remarks with respect to position. Contrary to most of the Anatince, the mantle of this animal is only closed posteally ; but this exception shows the value we set on the preceding- observation on the ossicle. Animal inhabiting a white shell, smooth at the umbones, and often roughened at the margins with minute points, of th of an inch transverse, and not quite T \jth vertical measure, with prominent pointed beaks, of oval shape anteally, and sub- angular posteally, which side is the shortest slope from the beaks ; in the right valve, close on each side the ossicular and cartilage-pit, is a strong triangular, flattish, acutely pointed cardinal tooth; in the left valve the central pit is without cardinals, but there are two rather distant obsolete laterals. L 146 ANATINHXE. The ground colour of the animal is hyaline white ; the mantle is considerably extended beyond the margins of the shell, and is of azure hyaline, edged with brilliant silvery, close-set, sym- metrical, blunt, short, but distinct dentations, which extend on both sides to near the beaks ; consequently it is open from the anterior side, throughout the ventral range, to the sessile anal tube, which is scarcely visible, being within the margins of the shell, from which we saw ejected the elongated oval drab pellets : this is the only apparent siphonal orifice. The foot is very large, long, broad, subtriangular, hyaline, well suiFused with flake- white points ; it is usually protruded in the centre of the ventral range, and the animal frequently passes it from stem to stern ; it is slightly geniculated and has a decided byssal groove. The animal is lively, marches with rapidity, and in its course turns from side to side, sometimes resting the shell on the ventral range in an upright posture. The branchiae and palpi, from their minuteness, escaped observation. It inhabits the coralline district at Exmouth, from which we have obtained many live examples. A. FERRUGINOSA, Montacuta ferruginosa, Brit. Moll. ii. p. 72, pi. 18. f. 5, 5 a & 5 b. My a ferruc/inosa, Montagu et Auctorum. This species has not occurred to us alive, and up to 1849 all the information obtained from naturalists was, that the foot is large, the posterior tubes absent, that it has only a sessile orifice, and that the anterior end of the shell is the longer side. But since that date, in 1850, we have had the advan- tage of seeing Mr. Alder's paper on the Montacuta ferruginosa in the ' Annals of Natural History/ N. S. v. p. 210, pi. 6. f. B. We collect from the account, that the mantle of the animal is considerably produced anteally, and fringed for a large por- tion of its extent. A comparison of these points with our own notes on the Anatina bidentata, which authors style Montacuta bidentata, of which we have examined many live examples, shows the concordance of the two species ; in both, the auteally produced and fringed mantle, the character of the foot, and ANATINA. 147 very similar hinge and dentition, have satisfied us of the family identity. Though, in our only specimen of the "fer- ruginosa" the moveable ossicle is not present, probably in consequence of its being removed with the animal, still we are convinced that in perfect and fresh specimens, opened with great care, the ossicle will be found ; the delicacy and fragility of this appendage are excessive, and though we have several of the A. bidentata in beautiful condition, ninety-nine out of a hundred cabinet examples will be found imperfect. Conse- quently being morally certain that the " ferruginosa " has the " shibboleth " of the Anatince, we feel justified in consigning it to that family, to range with its congener the A. bidentata. We cannot concur with Mr. Alder in recognizing that his Montacuta ferruginosa exhibits a connective gradation with Kellia, Lepton, and Galeomma. We think these genera are well distinguished not only from it, but from each other, and are absolutely of different family types. We hope our new locations and explanatory remarks on these genera will satisfy naturalists that every discordance exists between Lepton and Galeomma, with the "ferruginosa "; the strict Arcadan foot of the first two has no community with the common lingui- form pedal appendage of the latter, and all the other organs of one and the other are equally heterogeneous ; and lastly, we state, that the differences between Kellia and the "ferru- ginosa " are equally decisive. To prevent repetition, we only give short notes and refer- ences to the four remaining species of this family. A. DECLIVIS, Pennant et nobis. Thracia pubescens, Brit. Moll. i. p. 226, pi. 16. f. 2, 3. Anatina myalls, Lamarck. This is the largest British Anatina, being sometimes 3 inches transverse, and 2 of vertical measure. It differs in no essential point from its congeners except in size. It is a rare species, and it is difficult to obtain a suite of examples from half an inch upwards. It is taken in the coral zone at Exmouth, but rarely alive. L2 148 CORBULID.E. A. FRyETENUis, Pulteney et nobis. Cockleodesma, Couthouy. C. preetenue, Brit. Moll. i. p. 235, pi. 15. f. 4. As the animal of this species varies in no material cha- racter from our type, we refer to our account of it in the 1 British Mollusca/ which volumes we suppose to be in the hands of eveiy cultivator of this branch of natural history. The specialties of the shell are not of moment in a generic point of view. The ossicle is large, and more apparent than usual. A. DISTORTA, Montagu et nobis. Thracia distorta, Brit. Moll. i. p. 231, pi. 17- f. 1, 2, 3, 8 ; (animal) pi. H. f. 5. For an account of this animal, we refer to notes of ours in the ' British Mollusca/ The ossicle is the most minute of the tribe. A. CONVEXA, Wood et nobis. Thracia convexa, Brit. Moll. i. p. 229, pi. 16. f. 1 , 4. We have not seen the animal of this species, but cannot doubt that it marches with its congeners. We have shells in our collection containing the usual arcuated ossicle. Small shells are frequently met with at Exmouth, but those of 2 inches transverse measure are very rare. This little group consists of three genera, Corbula, Sphania, and Pandora ; the first has only one established species ; Sphtenia, one ; and the last, two ; one of which is probably not indigenous. The Corbuhdce, by the closed mantle and short united siphons, are allied to the Anatinidas and Saxicavce. COEBULA. 149 CORBULA, Bruguiere. C. NUCLEUS, Lamarck. C. nucleus, Brit. Moll. i. p. 181, pi. 9. f. 7-12; (animal) pi. G. f.3. Animal subtriangular, thick, yellowish-white ; mantle closed, except anteriorly, presenting an orifice having its circumference finely dentated, that marks the point of passage of a moderately long, subcylindrical byssal foot ; posteally it forms two short united siphons, each with 8-10 cirrhi ; the upper, or anal, has a hyaline, tubular, retractile, valvular, globular membrane, which is in frequent action, and appears to regulate the pro- pulsion of the fsecal matters, and the ingress and egress of the water for the various purposes of the animal oeconomy, which will be fully explained in the observations on the Pholadidce. On each side of the body there is a pair of very unequal branchiae, which hang obliquely, the upper being narrow, the lower larger and more triangular ; their colour brown, smooth on their outsides, and finely striated within ; on each side there are two long, narrow, pointed, brown pendulous palpi, pectinated strongly on both surfaces. Besides the red points circling the cirrhi of the siphoiial tubes, there is a dark line encompassing both at a short distance from the cirrhal circle of points ; these are better seen in the dead animal. The liver is black-green. We have taken, in the deepest part of the British Channel, conglomerations of many thousands of this species of all growths, having shells of brown and white, and often roseate hues ; they adhere to each other by fine silky byssal filaments. The C. ovata is a doubtful British species, and Mr. Wai- pole, of Monkstown, Co. Dublin, having favoured us with a specimen of his C. rosea, we can only consider it the common roseate variety of C. nucleus. Since the above remark, Mr. Walpole has informed us, that he has submitted specimens to Professor Forbes, who has come to the same conclusion. As to the C. ovata and C. rosea of the ( British Mollusca/ we supply the following references : C. HOSE A, Brown. C. rosea ? Brit. Moll. i. p. 185, pi. 9. f. 13, 14. C. OVATA, Forbes. C. ovata? Brit. Moll. i. p. 187, pi. 9. f. 15. 150 CORBULIDJE. SPH.^NIA, Turton. S. BINGHAMI, Turton. S. Binc/hami, Brit. Moll. i. p. 190, pi. 9. f. 1, 2, 3. Animal elongated, compressed, pale yellowish- white ; mantle closed, except a passage anteally for a small, narrow, sub- cylindrical foot, of a bluish transparent colour, with a byssus of coarse filaments, and another for the anal and branchial tubes. The anal siphon is short, but the longest of the two ; it is encircled by 5-6 rough white cirrhi, and emits a large, subhyaline, delicately frosted valve, which, on each step of the animal in advance, is considerably exserted, and then suddenly withdrawn ; the branchial siphon is little more than a sessile orifice, but in connection with the anal one, and, like it, furnished with 5-6 rough white cirrhi. The branchiae are of a pale brown, the under one being the largest, and runs horizontally ; the upper is much smaller, and laps on the other obliquely ; the branchial vessels are so minute as to give the laminse the appearance of smoothness ; there is, on each side, at least one subtriangular, pointed, well-striated palpum, and it is probable there is a second that has escaped detection. This animal has great affinity to Saxicava, besides alliances with Corbula and My a ; indeed the genus Sphcenia is almost unnecessary, as its animal is nearly identical with Saxicava arctica, and the structure of the hinge and the other hard parts have much the same generalities. In our dubiety whether this animal ought to be deposited in Sphcenia or Saxicava, we have cut the Gordian knot, by adopting, con- trary to our particular views, an almost superfluous genus, being in some measure stimulated to this resolve by the respect we entertain for the memory of our old talented friend Dr. Turton, its founder, whose numerous works are so highly valued by conchologists. PANDORA, Lamarck. P. OBTUSA, Leach et Auctorum. P. obtusa, Brit. Moll. i. p. 210, pi. 8. f. 5 ; (animal) pi. G. f. 10. Animal suboval, somewhat elongated ; the left side is more PANDORA. 151 tumid than the right : the mantle is closed, except a small fissure at the anterior end for the issue of the foot ; posteriorly it forms a sheath, which encloses the very short, scarcely separated siphons, that merely show their extremities, which are fringed at the orifices with fine white short cirrhi ; the margin of the sheath, in some specimens, is marked with a fine orange line, and the base of the cirrhi and margins of the ori- fices are usually encircled with a dead- white narrow thread. With regard to the branchiae, I have great satisfaction in stating, that after the examination of many live specimens, I am enabled to settle the true character of them. I have been most anxious on this head, as the statement in the ( British Mollusca/ pp. 210-212, is given from old notes of mine in 1835, in which it is observed, that there are two palpi and one branchial lamina. Later and repeated examinations require the following rectifications. I can now say, beyond dispute, and show the fact by preparations, that there are two palpi and two branchiae on each side of the body ; the branchiae run horizontally, being long, narrow, slightly arcuated, and symmetrical, pale brown, and pectinated by the blood-vessels on both surfaces ; their posterior points pass into the branchial tube; the palpi are short, small, pale brown, triangular, pointed, and striated transversely. The ovarium is orange-coloured, and placed posterior to, and in contact with, the dark green liver : in the genial months the ova, in all stages of development, are very conspicuous, which, we think, on exclusion pass, without any delay in the branchiae, into their native element. The intestine passes out of the posterior basal part of the liver to the bottom of the body, and then ascends under the branchiae and adductor muscle to its termination in the anal tube. This very elegant species, both as to the animal and shell, is sufficiently plentiful, alive, at Exmouth, in the coralline zone. P. ROSTRATA, Lamarck. P. rostrata, Brit. Moll. i. p. 207, pi. 8. f. 1-4. This species is an inhabitant of the Channel Islands ; we believe there is no well-authenticated capture of a live animal on the strictly British coasts. 152 SOLENKL3I. SOLENID^E. Agreeably to our method, this family contains only two British genera, Solen and Solenicurtus ; the first has five, the latter, two species. Solen is a singular genus, its transverse measure in some species being 8 to 1 of the vertical. The foot occupies one end of the shell, the buccal orifice the middle, and the posterior portion contains the short siphons, which are nearly united, except in S. legumen, in which they are somewhat longer and more divergent. They have alliances with the GastroclKenidce, and by the long linear branchiae with the Pholades ; but the ample notes on the principal species will give the necessaiy explanations. SOLEN, Linnaeus. S. SILIQUA, Linnaeus et Auct. S. siliqua, Brit. Moll. i. p. 246, pi. 14. f. 3; (animal) pi. I. f. 1. Animal subcylindrical, pale drab ; the mantle is yellowish- wliite, tumid at the extremities, swelling beyond the margins of the shell, closed throughout, except a central narrow rayed slit, which appears to have no other use than to admit water to the branchiae, in aid of the pedal orifice, which in this family is greatly contracted by the shape and position of the foot ; it is also produced into a siphon al sheath, truncate at the extremity, bordered by a fine brown line, and which contains two short siphons, just separate at their termi- nations ; they are never extended much beyond the shell ; the upper is rather the shortest, and of less diameter than the branchial tube ; it is encircled by two rows of irregular cirrhi, which do not quite reach the orifice, the margin of which is plain; the lower one has about twelve rather long, tumid, pointed, white filaments ; the upper, about twenty cirrhi, of three lengths and sizes, marked with fine brown lines and blotches at their bases, edges and summits; the branchial siphon has also two rows of similar cirrhi; in the lower one SOLEN. 153 there are about fifteen, and in the upper, thirty of different sizes. The foot is long, strong, muscular, and subcylindrical, fixed to the comparatively small body about the middle of the shell ; it has the power of changing the terminal portion into all shapes, from the fine elongated tentacular point, to the decided club-shaped extremity ; the foot, when half-extended, is oblique, and obtusely pointed ; the colour is pale yellow- white, marked for some distance anteally with exceedingly fine, very pale, close, lead- coloured lines. The animal has two systems of locomotion; the one for ascending from its deep perpendicular hole, the other for changing its locality, which it can effect by darting forward with a rapidity equal to that of the Pectines. The foot has a decided tubular aquiferous canal, from its junction with the body to within a short distance from the termination; the outer tissue appears homogeneous, but the entire conical cavity is furnished with strong elastic fibres, which doubtless have the power to close or greatly contract it. How the water gets access to the cavity is doubtful ; I coidd detect no orifice either at the point or junction with the body; one must suppose it to enter by the mouth, stomach, and walls of the crystalline stylet, and, from thence, to have a contact with the enveloping membrane of the viscera, if not an inward com- munication. What is the particular oeconomy of this sort of foot, which is in some measure analogous to that of the Lucince, only in them it is perforated throughout, is at pre- sent hypothetical. Can it be, in Solen, to give it increased power and elasticity, and in its deep hole of two feet or more, by a sudden compression to aid the muscular extension, which alone could not effect the ascent of the animal from its deep lodgement ? and is the cornpressive action also the agent to enable it, when out of its retreat, to dart with such unusual rapidity ? There are on each side a pair of equal-sized, long, linear, narrow branchiae, which, after getting rid of the interposition of the body, proceed, fixed to the roof of the long dorsal range of the mantle, to the branchial siphon, each pair united to the other, to deposit in it their attenuated points, as in the 154 SOLENID^E. Pholades. I believe there is no communication between the siphons, but I have not proved this fact by injections, as in Pholas. The branchial transverse vessels, artery, and vein are very distinctly marked ; there are, in connection with the laminae, a pair, on each side, of pale brown, thin, small, delicate triangrdar palpi, smooth without, striated within. The liver is composed of distinct aggregations of light greenish or yellowish masses, with the ovary united to it more anteally. The crystalline stylet is very long, but the tricuspid membrane or attritor is without much consistence ; it works, however, in the stomach. The general anatomy is in most respects as in Pholas, but it has two adductors, instead of the single post-medial one of that genus, and, as in it, the intestine plunges into the body, then ascends, and runs posteriorly on the dorsal range embraced by the heart and auricles, and discharges into the anal conduit by a white pendulous rectum. The branchial and anal siphons being short, may possibly be confluent as in the short-tubed animals, in which case the entire ventral cavity must be considered as one large branchial siphon, divided by a septum at their termination. This animal represents the typical Solens. We may observe, that the long branchial cavity in some measure supplies the place of the elongated siphons of the Pholades. S. PELLUCIDUS, Pennant et Auct. S. pellucidus, Brit. Moll. i. p. 252, pi. 13. f. 3; (animal) pi. I. f. 2. Animal elongated, compressed ; mantle of the palest drab, closed ventrally, without the central assistant branchial slit as in S. siliqua, open at both ends for the passage of the foot and siphons; these latter are very short, scarcely protruded beyond the shell ; the branchial has about ten cirrhi, edged with fine brown lines, with one or two smaller ones between each ; the anal tube is plain, or scarcely broken into points of a pale brown, and on both are a few large, rather long, white filaments, springing from the body of the common sheath, just below the siphonal orifices. The foot is much less SOLEN. 155 cylindrical than in S. siliqua, thus affording a sufficient pedal entry for the water, and is without the central fringed fissure of S. siliqua and S. ensis ; it is attached to the body about the middle of the shell, being obliquely truncate, and can, like its congeners, assume the pointed, lanceolate, or club- shaped terminus ; the colour is that of a pale morello cherry, of paler and intenser hues. The animal is capable of the most rapid locomotion ; I have seen it dart in a large dish with the velocity of the Pectines. It lives, as the S. siliqua, in a perpendicular hole, and, like it, uses its powers of locomotion to change its habitat. There are, on each side, a pair of pale drab, long, linear branchiae, the upper not half the depth of the lower one, and after leaving the body, they run, fixed on the long dorsal range of the mantle, and then unite and enter the short branchial siphon. There are also, on each side, a pair of small darkish-drab triangular palpi, smooth on the outer surface, and pectinated within. The liver is quite on the dorsal line, green and below it, in close connection, is the ovary, filled at this season (22nd July) with round, flake- white ova. The stylet and tricuspid membrane or stomachal attritor are present. The connecting strap-shaped labia of the palpi around the mouth are as in S. siliqua. S. ENSIS, Linnaeus et Auct. S. ensis, Brit. Moll. i. p. 250, pi. 14. f. 2. Animal elongated, subconipressed, that is, less cylindrical than in S. siliqua, but more so than in S. pellucidus; the mantle is open at both ends, and has the fringed central fissure, with the same character of the tubes, cirrhi, and colours, as in S. siliqua. The branchiae, labia, and palpi are proportionately the same; the foot, though less cylindrical, is capable of the same changes of form, but instead of being at the termination truncate and rectangular, it forms an oblique sweep ; and the colour at its extremity, in lieu of being pale cloudy- white, is studded with very minute papillae, and meandering red-brown lines in the interstices, only to be seen 156 SOLENIDJE. by a lens. The liver forms the same granular brown masses, connected anteally towards the lower part of the body with the ovary. The crystalline stylet or attritor is present. We may state, that excepting the narrower arcuated shell, lesser size, and the oblique termination of the foot, it is the prototype of the curved variety of S. siliqua. S. LEGUMEN, Linn, et nobis. Ceratisolen legumen, Brit. Moll. i. p. 256, pi. 13. f. 2; (animal) pi. I. f 4. This animal is subcompressed, and in comparison with its congeners only presents specialty-variations, the principal one being the greater extension, separation and divergency of the siphons. We do not see any sufficient character to remove this species from Solen. The undermentioned species, though occasionally taken alive at Exmouth, has not occurred to us. S. MARGIN ATUS, Pultcney. S. marginatus, Brit. Moll. i. p. 242, pi. 14. f. 1 ; (animal) pi. I. f. 3. SOLENICURTUS, De Blainville. S. COARCTATUS, Gmelui. S. coarctatus, Brit. Moll. i. p. 259, pi. 15. f. 3; (animal) pi. I. f. 5. S. antiquatus, Auctorum. Animal oblong, reniform, subcompressed, white throughout. Mantle closed, except anteriorly, for a large, thick, linguiform foot, and posteally it forms a common sheath, from which the siphons spring ; the branchial tube is only cirrhated at the ori- fice, and the animal often inflates both to three times the ordi- nary diameter. The branchiae are a pair on each side, long, narrow, attenuating posteriorly, and, as in the Pholades, are partly deposited in the branchial department of the siphonal sheath ; the corresponding pairs of palpi are long, slender, triangular, well-pectinated within, and less so on the outside. There is no byssal groove in the foot. This species has the greatest analogy to the Solcns, but subject to some modifica- SOLENICUETUS. 157 tions of the foot and shell, from which its generic appellation originates. Some malacologists have an idea, that this creature, and that of S. candidus, is too large for its habitation ; this is a mistake, which has arisen from the animal when in confine- ment exserting the belly of the mantle, inflated by water, beyond the margin of the shell ; but the instant it is irritated, it can place every organ a I'abri. S. candidus is in the same category as to this point. This account is partly from the recollection of twenty years ago ; there are gaps in it which we hope to make good. We have, though rarely, taken this animal alive at Exmouth. S. CANDIDUS, Renieri. S. candidus, Brit. Moll. i. p. 263, pi. 15. f. 1, 2. Solen strigillatus, Anglorum. S. scopula, juv., Anglorum. We have been favoured by Dr. Battersby of Torquay with fresh, though not live, specimens of this species. To describe it would be nearly a repetition of the notes on S. coarctatus. The only variation in the animal is its being of a flesh colour, tinged with orange. We have rarely dredged the shells of this species, but never with the animal, in the coralline district at Exmouth. Gastrochcena, Saxicava, Panopcea, and Venerirupis are the genera which receive the British species ; they are allied "to Pholas, by being borers, except perhaps Panopcea, and having their mantle closed ; they have also a similar siphonal appa- ratus, which according to their minor volume is as propor- tionately elongated ; but most of them differ in having the siphons soldered together, showing externally a depressed line of separation, and have not the appearance of being enclosed in a common sheath. 158 GASTKOCH^NID^E. The genus Petricola has been associated with this family. A couple of specimens of P. lithophaga have been forced into the British list which are from habitats altogether apocryphal ; the one is stated to have occurred in clay at Bristol, the other, from discharged ballast in Cork harbour, a most suspicious receptacle. Those who wish to see an account of this species may consult the ' British Mollusca/ i. p. 151, pi. 6. f. 9, 10; (animal) pi. G. f. 1. We believe it is not indigenous. GASTROCHvENA, Spengler. G. MODIOLINA, Lamarck. G. modiolina, Brit. Moll. i. p. 132, pi. 2. f. 5, 6, 7, 8; (animal) pi. F. f. 5. Animal clavate anteriorly, attenuated behind ; pale brown ; mantle closed, except an aperture in front for a small sub- cylindrical byssal foot ; the texture is thin on the dorsal range, ventrally extremely fleshy, being composed on the inner surface of thick muscular pale green folds and rugosities. M. Deshayes considers these substances secreting glands; others, as ovaria ; we concur with that naturalist, and think they may produce the matter for the linings, and the viscous fluid for the agglutination of the molecular particles used in the construction of the tubular dwellings of these animals, when they are not in calcareous deposits. The siphonal tubes are elongations of the mantle, soldered on each other nearly their whole length, which in the greatest extension are about three times the length of the shell, and are even longer in propor- tion than those of the Pholades. M. Deshayes observes, in his comment on Lamarck, that the tubes are very short when the animal is contracted ; but this is so in every other bivalve under a similar condition ; their colour is pale reddish- brown, and both orifices have short cirrhi of an intense rufous hue. The branchise are pale brown, suboval, hanging hori- zontally, of small depth, gradually becoming posteriorly more linear, having their terminations deposited in the siphonal tube ; the texture is thin, and they are finely pectinated on GASTROCH^NA. 159 both surfaces ; the pair of palpi, on each side, are subtri- angular, pointed, smooth without, but striated on the internal faces. I believe one of the objects of the folds in the ventral portion of the mantle is to give greater elasticity and strength to that organ, in rubbing out the habitations of these creatures when in limestone. Many conjectures have been hazarded, how the animals of Gastrochana, as they grow, form and increase their flask-shaped habitations of agglutinated particles of gravel, sand, and shelly spoil, when they are located in old dead bivalve shells. I think the solution of this point pre- sents no particular difficulty. The enlargement is effected, as in the shells of the ordinary bivalves, by the periodical additions of testaceous matter, and of internal lining, to the gradually progressive excavations or tubular constructions, until the animal comes to maturity. It is an error to suppose that an animal, at any particular stage of its increment, before it has arrived at the full size, becomes completely encased, and in consequence must find some mode to extend the dimensions of its habitation in proportion to its own in- crease; such an operation is impossible, except by chemical or mechanical means ; but absorbents and solvents, even if we admit their application to calcareous matter, and that they have a solvent power not subject to neutralization, certainly would have no effect on the tubes that are often formed, of flinty and corally spoil. We believe that the fact is, the animal in some deposits is never entirely enclosed before it is adult, and that it increases its incipient cavity from the point on which it is first cast by regular progression until full ma- turity, when a final closure takes place, which is the test that further enlargement has ceased. We consider these views are analogous with the doming of the shell of the Pholas papy- racea, which is delayed whilst the animal gradually enlarges its habitation until the full growth determines the final closure. The foregoing remarks have chiefly reference to the pear- or flask-shaped excavations and constructions in old bivalves. There is greater difficulty to account for the progressively 160 GASTROCH^NID.E. increasing enclosed excavations of the Gastroch MY A, Linnaeus. M. TRUNCATA, Linn, et Auctorum. M. truncata, Brit. Moll. i. p. 163, pi. 10. f. 1, 2, 3 ; (animal) pi. H. f. 1 . Animal elongated, subcompressed ; mantle pale brown, closed throughout, except an anterior fissure for a moderate tongue-shaped, yellowish-white foot, with a byssal groove, and being also produced into a long brown sheath covered with a dark rugose epidermis, under which the skin is white ; it can be extended to double the length of the shell ; when con- tracted it presents the aspect of a mass of close-set annular corrugations ; the sheath also contains the anal and branchial siphons, which are united to their terminations, and scarcely appear beyond the walls of the common envelope ; the former, besides the usual exsertile valve, has about fifteen short dirty- white cirrhi, with as many still shorter between them ; the lat- ter has twenty similar filaments, with intermediate short ones. There are on each side a pair of pale brown branchiae, rather narrow, the upper being somewhat less in depth; they are well pectinated on both surfaces, and their points enter the branchial sheath, but not to near the extent of the Pholades ; the two pairs of palpi are large, basally broad, triangular, of excessive thin texture, marked with fine short brown minute dots, and end in a sharpish point ; they are connected toge- ther by labia coasting the buccal orifice, and are visibly pec- tinated 011 both sides. The liver is dorsal, granular and yel- lowish-green, having the ovarium in contact anteally and ventrally. The stylet and stomachal attritor are present. This animal is a littoral species, inhabiting the shingle, and the sandy estuaries. It is also taken alive in the coralline zone. Bath, 21st January, 1851. I have stated above, that the foot has a byssal groove ; a careful examination of a lively specimen sent me this day from Exmouth, proves that I was mistaken ; the foot, though rather smaller in proportion than in the next species but one, the My a oblonga, nobis, the " Lutraria " of authors, is, like it, without a trace of byssal groove ; the branchiae and palpi of our present species, the type of the family, present the same 166 MYADJE. characteristic form and appearance as in the so-called Lutraria oblong a and L. elliptica. M. ARENARIA, Linn, et Auctorum. M. arenaria, Brit. Moll. i. p. 168, pi. 10. f. 4, 5, 6. We have not observed this species, but the recorded ac- counts of it show that it differs little from the type. Having ventured to consider Panopeea a superfluous genus, it is impossible that we can for a moment conscientiously maintain a still more unnecessary one, the " Lutraria " of authors ; our description will show that the present animal is in all essential points a My a ; the differences of the specialties of the soft parts are scarcely worth notice, the cirrhi being red-brown instead of white, and the terminations of the siphons slightly forked, whilst in the type, the M. truncata, there is no separation. The greatest variation between the two is in the hard parts, but I trust, at the present epoch, we are not to adopt precepts of zoology which would be incom- patible with the present position of the sciences ; that because an animal shuts the door of its house by a different-shaped hinge from that of its congener in all other respects, it is to be considered, on that account, generically distinct : we may as well say of two similar doors, that because one has the patent hinges and the other the common sort, they are distinct kinds of objects ; it is the same with the M. oblonga : gentlemen may call its animal by the name of Lutraria, but that does not make it less a My a. We maintain the position that there is not a trace of generic distinction between the typical Mya and the so-called L. oblonga and L. elliptica, and that there are no more decided specialties between them, than between the species of every other genus. Lutraria has not a inalacolo- gical support ; it entirely rests on the artificial grounds of variation of the dentition of the hinge ; for the ligament or cartilage is what is called internal, both in Mya and Lutraria ; we therefore consider that an essential service is done in pro- posing to relieve science of a useless genus, which has not MYA. 1(57 even the excuse of an extraordinary number of species as a sort of palliation for its constitution. M. OBLONGA, nobis. Lutraria oblonga, Chemnitz. -, Brit. Moll. i. p. 374, pi. 13. f. 1. Mactra Mans, Mont, et Auct. Animal oblong, tolerably thick, very pale yellow, with the mantle closed, except a large anterior fissure for the foot ; it is also produced into a large, rugose when contracted, sheath, but not so much so as in M. truncata. The ground colour is white, but covered with a brown epidermis, which also is deposited on the ventral regions of the mantle ; the common sheath, containing the two siphons, can be greatly inflated, and is often extended twice the length of the shell ; it only just bifurcates at the terminus, showing the orifices of the siphons ; the anal is of much less calibre than the branchial, and encircled by 30-40 short, fine, simple, red-brown cirrhi ; the branchial has about the same number, of similar colour, half of which are stronger and longer than the others, being fimbriated on each side ; the remainder are interstitial. The foot is large, rather fleshy and linguiform, white, with a tinge of pale brown, and without a byssal groove. On each side there are a pair of branchiae and palpi ; the former are narrow, not strictly linear ; the upper one is not so deep as the under one anteally, but posteally they are much of the same dimen- sions, having their points deposited in the branchial siphon ; they are pale drab, with the transverse vessels of the circulation well marked on both sides. The palpi are very large, triangular, pointed, of very thin membranous texture, pale brown, and elegantly aspersed with minute red-brown points; the two pairs are united by plain labia passing around the mouth. We have taken this species at Exmouth alive : though very large valves are taken in the dredge, and continually cast on shore, it is singularly scarce, probably inhabiting the littoral limits, and lodged so deep as to escape detection and the action of the dredge. The above is taken from a fine 4-inch spe- cimen sent me to Bath, this 21st January, 1851, having been 168 cast on shore at Exmouth during the late gales ; it arrived quite lively, wrapped in fucus, and accompanied by sea-water. It proved an important acquisition. I ascertained, both anatomically and practically, that there is no connection between the branchial and anal siphons, affording another proof that there is an end to the doctrine of separate branchial currents by cilia. M. ELLIPTICA, nobis. Lutraria elliptica, Lamarck. -, Brit. Moll. i. p. 3/0, pi. 12 ; (animal) pi. H. f. 2. Mactra lutraria, Auctorum. Animal compressed, subovally elongated, white. The mantle, ventrally, has the margins united by a fine, white, minutely crenulated line, which marks the suture, except for a space of about one-third of the posterior portion of the pedal fissure, which is edged by rather distant fine white filaments, and affords a passage for a large thick tongue-shaped white foot, without a byssal groove. The siphonal sheath is very large, subcylindrically tapering, and, in a shell of 3i inches trans- verse measure, is, when in full activity, 6 inches long ; from its base for 2 inches it is white, and for another 2 inches marked with zigzag purplish-brown blotches, which at the terminal portion become distinct, dark purplish-brown dots; on the surface of the sheath there are two or three circular brown lines, an inch apart, and it is covered Avith a transparent corrugated skin, which appears to be a prolongation of the light horny epidermis that clothes the exterior of the entire area of the valves; within the sheath are the anal and branchial siphons, both furnished at their terminations with numerous white cirrhi, minutely spotted with dark purplish- brown or red ; the branchial cilia are the longest, delicately fimbriated 011 the margins Avith alternate smaller and shorter ones ; the anal are of the same colour, but shorter and more numerous. The branchiae are pale brown laminae, not deep, the upper ones being rather the lesser ; they are hung trans- versely, with their points lying in the branchial caAdty; the minute vessels of the circulation give them the appearance of 169 fine pectinations ; the pairs of palpi, which are pendent from each side the buccal orifice, and united around it by a mem- brane, are paler than the branchiae ; they are long, triangular, pointed, of fine texture, and delicately striated. All the Myce exsert from the anal siphon the usual tubular hyaline valve. This species inhabits the low-water levels of the littoral zone, in the loose sandy districts, and are enabled, by the powerful foot and siphonal sheath, to bury themselves more than a foot in depth. It is also taken in the corah 1 ine zone at Ex mouth. PHOLADID.E. Pholas, Teredo, and Xylophaga constitute the British ge- nera of this family. I have submitted the Pholades and the Teredo meyotara to a close examination, not only of the ex- ternal organs, but I have entered into detailed observations on their anatomical structure. Grave errors exist in our records relative to this family, both as regards the shells and the functions of the soft parts. It is really strange that in so celebrated and ancient a genus as Pholas, so often the theme of discussion, so many doubts and contradictory accounts should still prevail respecting the hinge, cartilage, ligament, and adductor muscles of the animal. Though there may be many errors, I think that malacologists will find, in this account, some rectifications, obscure points explained, a variety of new matter, and that the observations on the structure of P. dactylus and Teredo megotara will assist not only to illustrate this family, but, mutatis mutandis, give a general view of the material points of the organization of the animals of the Acephala. As I have, in the accounts below, entered so largely into the incidents of this group, I shall at once plunge " in medias res." The first animal has caused great discussion, whether it ought to form two distinct species or only one, by considering its very different aspects as identical. We think it will 170 PHOLADID.E. appear that only one species exists ; but that malacologists may judge, we give specific descriptions of the two phases, the one being called Pholas papyracea, the other, P. lamellata. PHOLAS, Linnaeus. P. PAPYRACEA, Solander et Auct. P. papyracea, Brit. Moll. i. p. 123, pi. 5. f. 3, 4, 5, 6, and pi. 2. f. 1 ; (animal) pi. F. f. 4. Animal elongated, subcyliudrical ; mantle closed, except a small rayed aperture for the foot, as long as one exists, and which corresponds in position with a similar aperture in the membrane connecting the doming of the shell, and is styled by Dr. Turton a " spiracle/' but which may perhaps in this species, the only one of the Pholades that has it, be for the purpose of a partial issue, or rather protrusion, without the solution of continuity of the ventral membrane of the animal, of the hyaline cylindrical appendage which exists in all bivalves, to secure for it a point of support when the foot becomes so much diminished as not to afl'ord one. In all other bivalves this stylet is not visible, being imbedded in the body and upper part of the pedicle of the foot, which is the leaning- stock or point of resistance, except in the Anomice, Ostrece, and Pectinidce, in which, as the foot is reduced almost to nothing, the mass of the body is the only point d'appui but when the dome of the shell of the Pholadidea papyracea is removed, the dark basal point of the stylet presents itself in the centre of the mottled belly, precisely where the foot is placed in the group of the Pholades ; or the fissure may be, for flux and reflux of the water for branchial purposes. The siphonal apparatus consists of a long elastic sheath, which is often protruded to double the length of the shell, but in a state of half- extension it becomes highly corrugated ; it is clothed with a dull red-brown epidermis, under which it is bluish- white ; the margin of its terminus is finely fringed with short white cirrhi ; within the sheath are the anal and branchial tubes, the former with the margin quite plain, but PHOLAS. 171 with an exsertile tubular hyaline process ; the latter is encir- cled by about twenty white cirrhi of different lengths. The liver is green, and situated as usual on the dorsal range. There are on each side of the body a pair of pale reddish-brown elongated suboval branchiae, the upper one being much the smallest, which are finely striated on the outer surfaces ; their posterior extremities suddenly become linear, and are then deposited in the branchial tube ; there are also two long flat linear palpi on each side, with lanceolate points; these are more striated than the branchiae. The body is centrally sub- globose, but tapers posteally and anteally to a blunt terminus, and the whole of it presents, especially in the genial season, a mottled mass of flaky-white subrotund spots or dots, with one of the termini of the elastic appendage appearing in the centre of the anterior extremity. With regard to the foot, as I have already observed, not a trace is visible, having vanished for reasons to be spoken of below. P. PAPYRACEA, JUV., Pholadidea papyracea, Brit. Moll. i. p. 123, pi. 5. f. 3, 4, 5, 6 ; pi. 2. f. 1 ; (animal) pi. E. f. 4. Pholas lamellata, Auctorum. Animal nearly of the form we have just described ; mantle closed, except a large aperture for the passage of the foot, which in this form of the P. papyracea is most apparent. The branchial processes and siphonal tubes are, in the most minute points, similar to those organs in the form styled Pholadidea papyracea, to which we refer ; the body, as in it, is subglobose, and produced posteally and anteally to an obtuse point, and it is generally of a bluish-hyaline colour, with some fine anastomosing lines throughout its surface, but has nothing of the mottled appearance of Pholadidea papyracea ; the shape of the branchiae is the same as in its congener, but their striae are more delicate and colour of the palest yellow ; these are the mere variations of adolescence, and generally prevail where specific identity cannot be doubted, and they are deposited partially as in its congener, in the branchial tube : the palpi and liver exhibit no variation. 172 PHOLADID^E. I now come to the most decided difference between the two animals ; the foot, in the form we are now describing, is proportionally larger than in any other of the Pholades, of hyaline texture, springing from the centre of the body with a long cylindrical pedicle; it has a subclavate appear- ance, truncate at the terminus, which is of suboval form and pointed anteally and posteally, and there is no outward visible trace of the curious elastic stylet common to all bivalves, and so conspicuous in the ventral tissue of the form Pholadidea papy racea. I will now make a short comparison of the two forms : it will be observed that it is stated, in the form Pholadidea papyracea, that the mantle is closed, except a very small aperture or " spiracle " for the foot, if it still exists ; but in the form Pholas lamellata there is a large aperture for a foot, that is, larger in proportion than in any of the Pholades. The branchiae, palpi, and elaborate siphonal apparatus are precisely the same, with only variations of colour ; the bodies of the two are of the same shape, but differ in colour and markings, the one being intensely mottled, the other hyaline ; the body of the one having no foot attached to it, but the other a very large one. These are the principal variations, and certainly constitute a very general difference of aspect between the animals of the two forms, and it must be admitted that conchologists and even malacologists, who have not examined with care all the conditions and incidents attached to them, have had a primd facie case for doubting their identity ; but notwithstanding these great and visible discre- pancies, I think I shall make out a case of identity. In the course of my examinations I was startled by the great variations in the organs of the tAvo forms of this Pholas, which, twenty years ago, when I first examined this species, appear not to have so rigorously excited my notice ; doubts arose in my mind, that I might be wrong in my former determinations of identity, and I wrote to Dr. Battersby to express them to him and Mrs. Griffith, both of Torquay ; the latter a lady naturalist, who has taken great interest in this question; but in the summer of 1849, after a continued in- PHOLAS. l/ a vestigatiou of fourteen weeks, my doubts were dispelled, and I stated personally to Dr. Battersby, that after a careful review of all the evidences that presented themselves, I re- verted to and relied on my original determination of identity of the two forms of Pholadidea papyracea. This change of opinion arose from the observation that in the adult Pholadidea papyracea, the mottled appearance of the belly, so dissimilar to that of the form Pholas lameUata, was due to the extension of the reproductive membranous organs of the ovarium occupying the space usually appropriated to the foot, which I found had disappeared. This anomalous appearance excited my attention, and the reflection that with nearly absolute cceteris paribiis in the generalities of all the Pholades, there was no substantial reason why one species should always be deprived of the foot, when all the others possessed that appendage, and as I had come to the conclusion that it was the boring instrument, I felt assured that this anomaly was only an apparent one, dependent on certain conditions connected with the growth of the animal. And as the very large anterior gape in all the Pholades is the site of the powerful foot, and is never closed up during their exist- ence, except in this species, I became fully convinced that the foot, having finally performed its terebrating functions, the animal consequently having arrived at full growth (the test of which is the doming and formation of the caliciform incipient tubing, which is in Pholadidea papyracea the last vestige of the protecting tubes of the Teredinida;} - - had become absorbed, on the well-known principle, that an organ from want of use is often, especially in the lower animals, followed by its total disappearance. I have already shown that the great variation in colour and markings between the adult Pholadidea papyracea and the young shell styled Pholas lameUata is the effect of generative influences, and that its conspicuous foot, when it arrives at full growth, which is testified by its becoming completely domed, is depauperated and finely obliterated. These two great and principal variations of aspect between the two forms of Pholadidea papyracea, resulting from states of transition, 174 PHOLADID^E. having I trust been satisfactorily disposed of, and every other part of the animal exhibiting a prototype similarity, it is impossible, as I think, to entertain further doubts of the positive identity of the two shells usually termed by authors Pholas papyracea and P. lamellata. I may add, that it has been asked in objection, how is it that twenty Pholadidea papyracea are taken for one Pholas lamellata, and that the two forms are not more frequently met with in the transition states? This objection quickly yields to a just view of the Pholades as regards habitat and other influences. The great mass of the Pholades inhabit the littoral and laminarian zones, and are thus open to the attacks of a multi- tude of enemies ; the delicate young papyracea suffer severely. My dredger, who for more than forty years has annually dug large quantities of all the species except P. crispata, states, that he constantly finds the shells of the young papyracea in their cavities, cleared out of the animal by minute species of Crustacea, in such quantities, that the dealers set them up with gum as a substitute for the rarer live examples, but the domed shells are rarely met with ; still a portion escape to maintain the race, and some few young occasionally occur. I have personally taken them, in situ, in a decided transition state; it is necessary to observe that the crafty dealers produce this condition by mutilating the dome, but a lens will show the artful fracture or the natural progress of growth. I will say a few words on the pelagic Pholades inhabiting masses of stone dredged up in the littoral zones of the Devon coasts, six or eight miles from land. These shells, whether they are the two forms of Pholadidea papyracea, or the Pholas parva or P. dactylus, are always dwarf. I have a curious series of minute and completely adult Pholadidea papyracea not exceeding a of an inch in length. Such shells are considered by the inexperienced observer as proofs that at all ages the Pholadidea papyracea is completely covered with a dome and continues gradually to increase : this is impossible, as when the dome and caliciform posterior extremity are once formed, all further growth is for ever terminated. The pelagic PHOLAS. 175 Pholades rarely exceed | an inch in length, consequently these dwarf forms are the result of locality, depth of water, and many other conditions. In the deeper zones, the young forms of the present species, instead of being found in the proportion of one to twenty of the adult shells, appear in equal numbers : this discrepancy in the proportions of the young shells in- habiting the littoral and pelagic zones, must arise from the circumstance that in the deeper waters there is more room for reproduction, more sustentation, and fewer enemies ; this view corroborates the doctrine above, accounting for the disparity of numbers in the littoral zones between the young and old shells of this species. P. DACTYLUS, Linnseus. P. dactylus, Brit. Moll. i. p. 108, pi. 3. Animal conically elongated ; body pale bluish- white ; mantle tinged with yellow, very thick ventrally, posteally, and around the gape; the other portions are of the thinnest texture, closed throughout, except anteriorly a large oval aperture for the passage of the foot, and having the posterior end produced into a long retractile sheath of a milk-white colour when denuded of the epidermis, enclosing the branchial and anal siphons, which are just separated at their termini, the former with 12-16 long cirrhi, usually furnished on one side, some- times on both, with 3-7 fimbrise, besides one or two inter- mediate shorter cirrhi, which are ciliated on both sides. The anal tube is plain and slightly escalloped, but in some states it appears to have a number of short blunt cirrhi, which are not real, but occasioned by the doubling of the points of the scallops on contraction ; their colour is brown, interspersed with a few white blotches, producing a pepper-and-salt ap- pearance ; the sheath for a short distance from the terminus is studded with subcircular whitish squamous papillae . The foot is plain, hyaline, bluish-white, suboval, pointed before and behind, truncate basally, rather obliquely fixed to the body by a long cylindrical, thick, fleshy white pedicle. The sheath can be extended to double the length of the shell, and the branchial portion is often distended with water to three 176 PHOLADHXE. times the usual size; its diameter greatly exceeds the anal one. There are on each side of the body a pair of long nar- row symmetrical branchiae ; these are nearly of similar size, reaching fully to the anterior end, from which they taper gradually posteally, and lie, not free, but fixed throughout their extent to within ^ an inch of the branchial compart- ment ; they are pale brown ; the branchial vessels are trans- verse, large, but not crowded, and present the aspect of coarse pectinations. On each side of the body there is a pair of the palest bluish-Avhite, large, subsymmetrical, fleshy, pointed palpi, representing very elongated triangles ; each pair is con- nected with its correspondent one by fillets above and below the mouth; they are strongly obliquely striated, as well as reticulated, though irregularly, on the inner surface by the vessels of the circulation ; on the outer side the striae or reti- culations are not apparent. The branchiee at their anteal angles effect a contact with the palpi at their posteal points. The outer palpum of each pair appears rather less, and more laminar than its fellow. These appendages are usually con- sidered to be of a tentacular nature, to conduct the aliment into the mouth : they may be ; but they have also branchial functions, as they are connected with each other by a very visible artery that coalesces with that of one of the main branchiae, and I have not a doubt that leading branchial veins form a similar union with those of the regular branchiae. The liver is anterior, of ample volume, granular, and yel- lowish-green. P. PARVA, Pennant. P.parva, Brit. Moll. i. p. Ill, pi. 4. f. 1, 2. pi. 2. f. 2; (animal) pi. F. f. 3 & 3 a. Animal thick, subcylindrical, less elongated than its con- geners; body milk-white; mantle pale bluish-white, when deprived of the fugacious light-red epidermis, which, at the closure of the valves, forms a line resembling a suture of a red sandy colour : this division of the body causes each side of it to appear banded. The mantle is closed except an aperture for the foot, and is prolonged into a long retractile sheath PHOLAS. 177 covered with a thick red-brown epidermis, which is aspersed with thick-set sand-like red eminences,, or minute papillae, that become larger and more intense at the termini of the orifices, where its margin is irregularly encircled with a fine light brown fringe or rather pile; within the periphery of this fringe are the siphonal apertures, the branchial one being rather the longest, without cirrhi, but sinuated or escalloped, and marked with a dozen brown and white alternate lines running into the tube; these at half-contraction have the appearance of short blunt cirrhi, occasioned by the doubling of the brown and white points of the scallops, the two nearest the anal tube being the longest in appearance, with a single one exactly opposite the two; these however are only de- ceptions, and vanish entirely when the tube is fully expanded ; the anal cylinder is pale brown and perfectly simple ; both siphons are destitute of cilia, having only the margins of the sheath finely pilose ; none of the other Pholades are without cirrhi on the branchial orifice. The foot, when at rest, is nearly an oval, but in action it becomes pointed behind and rounded in front ; it is truncate at the base, and fixed to the body by a long round cylindrical fleshy pedicle of a pale bluish-white colour. The branchiae and the palpi on each side are so nearly similar to those of P. dactylus as to require no observation ; the siphonal sheath when extended is double the length of the shell. The liver is darker than in the last species. P. CANDIDA, Linnaeus. P. Candida, Brit. Moll. i. p. 117, pi. 4. f. 1, 2. Animal conically elongated from the anterior end to the posterior axis of the cone. The body, sheath and mantle are a pale red-brown, but when divested of the epidermis, of the palest hyaline tinged with brown. The mantle as usual is closed, except the aperture for the foot, and being produced into a sheath that is proportionately shorter than in its con- geners; the siphons are of the same length, and both are cirrhated at their orifices, the only example in this respect that we know of amongst the Pholades the branchial with N 1 78 PIIOLADID,. about twelve whitish-brown rays, of deeper tint towards the base, and between some of them one or two smaller, but not fimbriated ; the anal has about eight short pale rays. Some authors describe papillae on the tubes; our specimens only showed minute sand-like points, which we think are due to the epidermis. The foot is much narrower, more elongated and pointed than in any of its congeners, and fixed to the body by a compressed pedicle, of a pale hyaline in some animals, and flaky bluish- white in others. All the other organs exhibit no particular variation from those of P. dactylus. P. CRISPATA, Linnaeus. P. crispata, Brit. Moll. i. p. 114, pi. 4. f. 3, 4, 5. This Pholas does not inhabit the South Devon coasts. The P. striata of authors is exotic. I have so fully entered on the boring qualities of the Pholades in the January Number of the ' Annals' for 1850 as to render further remarks unnecessary. The Pholades are generally excavators and inhabitants of rocks, chiefly the red sandstone on the South Devon coast, but the P. dactylus and P. Candida often burrow and pass their existence in pure sand, at the back of the Warren and Cockle Sands at Exmouth, where the finest and most delicately sculptured individuals are found, surpassing in beauty the rock specimens. Having concluded my remarks on the external organs of the Pholades, I shall now proceed to the anatomy of the Pholas dactylus, connecting with it the parts of the shell that relate to the hinge, cartilage, ligament, curved subumboual apo- physes, and other accessories : for reference, and to prevent confusion, I have distributed the matters to be considered into distinct sections. The Hinge. The hinge of the Pholades appears not to be well under- stood, and has not received the investigation that has been so liberally bestowed on the terebrating powers of the animal ; PHOLAS. 1 79 it is extraordinary, even in late malacological works, to find it described as obscure and rudimental, and M. Deshayes, in his comment on Pholas in the last edition of Lamarck, mentions the hinge as scarcely existing, and not being a ' veritable ligament '- -how different from the fact ! If there is a genus better provided than any other of the bivalves with ligamental appendages, it is Pholas. The hinge of Pholas dactylus has very slight traces of denti- cular assistance ; it nevertheless works en charniere, in a circumscribed space, to which it is confined by powerful liga- ments, and though somewhat different in its component parts from the usual configuration, it does not in its functions materially differ from those of the ordinary bivalves ; it has a strictly internal cartilage, which is laminar, of small volume, oval shape, and light yellow colour ; it is fixed on the internal portion of the convexity of the valves, termed the hinge, which articulates, imbedded in the thin plates of the cartilage. The ligament succeeds ; it consists of two parallel plates, between which is a considerable interspace of strong, close-set, white, elastic transverse threads, the one fixed more externally to the inner side of the reflected dorsal cellular excrescence, the other, below it, to the internal commissure of the two valves ; thus forming a powerful ligament that allows them the usual movement of the ordinary hinge : on this is added a third ligamental apparatus, which may be termed accessorial, to in- crease the strength of the hinge, and which is formed by the reflection of the tough end of the mantle issuing between the anterior points of the valves in an elongated oval form, and covers the transverse threads of the outer layer of the liga- ment ; it is firmly secured by throwing out filaments which enter the dorsal cells of each valve : this production of the mantle is further fortified by two thin, flexible, suboval testa- ceous plates, supported by a subtriangular rest ; these appen- dages are exudations from the reflexed mantle. The posterior part of the valves, as is usual in elongated shells, has the common continuous membranous ligament produced by the protrusion of the edge of the mantle, with the addition, in this species, of a long thin linear testaceous plate ; the use of N 2 180 PHOLADUXE. this posterior ligament is to assist in maintaining the valves in their natural position. It appears then that Pholas is iron- bound as to ligament, which, in it, is far more powerful in securing the valves than in the shells of any other group of the Acephala of similar fragility and tenuity. The Muscular System. It will now be convenient to notice the muscular system : / arid in the first place, that part of it connected with the shell. In this group of bivalves, the curved spatulate apophyses springing under the umboiies have long excited the attention of naturalists, and the uses assigned to them as supports of the body, we believe to a certain extent to be correct; but they have other important functions that have not attracted sufficient notice. Before they are mentioned, it will facilitate their illustration if it is now stated, that though an anterior adductor muscle is spoken of by authors, there is not a trace of one in Pholas dactylus, and I believe all its congeners are also deprived of this organ. There is only one adductor muscle in Pholas, not posteriorly situated, but very slightly post-medial : the fact of the absence of this organ anteriorly, I think I have ascertained beyond doubt : no muscle passes through the animal or embraces the mantle anteally, the tough and thickened margins of which are supported on both sides the shell and around the gape by long thin strap-shaped fillets thrown off from the medial adductor muscle, which, with that of the foot, may be con- sidered as the great points of departure of all the principal muscles of the body. Some authors contend that what I call the ligament, under the dorsally reflected mantle, is the anterior adductor : this idea cannot be supported, as independent of this strange posi- tion for an adductor muscle, the two layers of filaments are fixed, the one external to the other, with a space between them, to the shell, and not to the animal ; therefore they are ligamental, and their action and reaction have the same effect as in the ordinary bivalve ligament. The important functions of the crotchets under the beaks PHOLAS. 181 claim particular notice, as much error has existed with respect to them : their utility originates from the two very strong muscular bands given off from the foot, which are fixed to their spatulate roughened terminations, and serve as points d'appui for its action in the work of excavation, without en- dangering or distressing the body. We have here a beautiful illustration of the resources of nature to accomplish what is necessary for the well-being of her creations ; for if the foot was attached to the body as in the ordinary bivalves, without aid, the severe action of excavation would probably paralyse the animal and tear it from its natural position, which result is prevented by this admirable contrivance, and the body lies securely supported in the curvature of these appendages, whilst the movement of the foot is altogether maintained by working from the crotchets. Nature has not given this animal an anterior adductor, bscause it is unnecessary, as it rarely expands the large gape by a separation of the valves ; and when it does, the medial adductor and the limited action of the ligament suf- fice : the permanent gape is the equivalent for what in ordi- nary bivalves is effected by the opening and closing of the shell by the adductor muscles. The apophysary and pedal apparatus are not the substitutes for an anterior adductor muscle ; for if they did act as such, their muscular powers must remain in quietude from the necessary contraction, and the excavating action would be destroyed : the two actions are completely antagonistic. The posterior part of the valves is only opened slightly to allow the issue of the basal portion of the branchial sheath, to assist by attrition in the enlarge- ment of the posterior part of the chamber whilst the foot is operating in front. The foot and pedicle, which in a living state appear almost hyaline, when they have become exsiccated, will be found to consist of a mass of longitudinal elastic fibres, the principal portion of which centre on the umbonal excrescences, and the remainder supply muscular threads to the anterior part of the body : the basal area of the foot is by far the most coriaceous portion. PHOLADID.E. Lamarck's Dimyal arrangement is strictly untenable, as the Pholades, having only a medial adductor, ought to be removed therefrom, and many of his Monomyce, having two muscles, must be deposited therein. The medial adductor of the Pholades is a most influential organ ; it is fixed to and is an integral component of the mantle at that point where it becomes the origin of the siphonal sheath, and adheres by its large subcircular flaps to each side of the valves, showing when removed two well-marked cicatrices : this muscle extends its influence to each extremity of the animal, as from it the man- tellar marginal supports emanate ; it also supplies the siphons with powerful retractors, and furnishes the tube into which the rectum discharges with a sphincter ; it is the main support and connection of the animal with the posterior part of the shell ; it likewise supplies the posteal parts of the body with the minor muscular threads ; and finally it is the organ of a limited relaxation to allow the valves to be opened in concert with the cartilage and ligament for the issue of the basal portion of the branchial sheath, when it is required to assist in excavation, and of their closure to expel the water from the respiratory sac. The whole mass of the branchial and anal tubes is a tissue of coriaceous muscles which are composed of layers of strong close-set longitudinal fibrous cords, crossed at right angles by minor ones, and at the posterior extremities they throw off the special annulated retractors of the terminal cirrhi of the branchial orifice, which appear each to have a minute sheath, and they also provide for the retraction of the anal orifice. We have next to examine the nervous influences. Nervous Influences. The powerful and diffusively distributed muscles of this species would lead us to expect that the medullary masses would be of corresponding importance ; this is not the case, as in Pholas dactylus I can only find two inconsiderable ganglia ; the anterior one is the largest, consisting of a white pulpy mass, situated on the centre of the oesophagus just above the buccal aperture ; from it two distinctly visible threads curve PHOLAS. 183 anteriorly, the one giving filaments to the right, the other to the left palpum, from whence additional ramifications proceed to the anterior parts of the body, besides supplying the muscles of the foot. The posterior ganglion is situated between the heart and the anus, and is connected with the anterior one by two close, parallel, dorsal, very minute longitudinal threads that are seen without difficulty, and cannot well be mistaken for veins ; the minor mass furnishes threads to the adductor muscle, and sends to the ovarium and muscles of the belly appropriate filaments. This is all that I have been able to observe of the nervous system, and collect from it, that how- ever insignificant the ganglionic masses may appear, their effects on the muscles prove that the potentiality of their in- fluences is not impaired by the minuteness of the hair-like threads which are the conductors of the subtle fluid that excites their action. T7ie Digestive Organs. We commence with the mouth, situate immediately above the connecting labium of the palpi ; it is rather a large trans- verse orifice, and leads directly into the simple oesophagus, which proceeds with a portion of the liver on each side of it through the anterior part of the dorsal range into a small oval stomach, the base of which is enveloped by the light green granular liver which pours 'the bile into its rigid coat by several ducts ; its cavity is almost filled up with a folded plate, which I call the gizzard or stomachal attritor, and authors the tricuspid membrane, which is erroneously, as I think, considered by some malacologists an agent to regulate the entrance of the bile from the liver. I think this idea cannot be sustained, as besides the stomach being provided with bile ducts, one of the axes of the tricuspid corneous plate is fixed at the cardiac orifice of the stomach, and receives the animal - culse as they descend the oesophagus ; and after trituration by the gizzard, which is worked by the elastic hyaline stylet, they pass through the other axis of the tricuspid membrane, which is inserted in the pyloric orifice into the intestine. I have preparations showing the gizzard in the stomach with its 184 PHOLADHLE. posterior end united to the intestine, and attached by the middle to the hyaline stylet. This singular organ, so well known to exist, I believe, in all bivalves, has caused some difference of opinion as to its use ; but I think when all the incidents attached to it have been mentioned, they, in conjunction with the position in the stomach of the tricu&pid organ, can lead to no other conclu- sion than that the apparatus is a gizzard worked by the foot and elastic stylet to comminute the food, and is analogous to the gizzard in many of the Gasteropoda. The stylet is for the basal half cylindrical, and tapers from thence to the stomach, where it makes a loop, and is fixed by a filamentary muscle to the gizzard or tricuspid membrane ; its colour is hyaline milk- white, and in certain lights reflects the metallic hues ; the working point of support is the centre of the basal part of the foot, through the pedicle of which it proceeds obliquely to the stomach, guarded by a sheath which appears to secrete a lubricating fluid, probably having its source from the liver, through the centre of which it passes to its junction with the corneous attritor ; it is eminently elastic, formed of a suite of circular lines ; it is impervious. I have submitted it to every sectional form, but the only departure from homogeneity are the fine circular elastic fibres ; in the species we now describe it is fixed by a short muscle to the bottom of the foot ; in P. parva it appears to rest, free. At one time I thought the stylet might be the vehicle of a solvent fluid from the stomach, but its impermeability negatives this idea ; and if there is a connection with the foot from the stomach, it must be by the sides of the walls of its sheath ; in that case a solvent would neutralize the lubricity so necessary to its action, as a spring for the gizzard ; besides, the most careful examination of the external and internal surfaces of the foot shows no connection between them, or orifice for the issue of a solvent. No ad- juvant powers of sight have enabled me, in this species, to discover the pore which is said to admit water to the foot of many of the bivalves, or to expel it if received from the stomach. 1 now return to the intestine, which we left united to the PHOLAS. 185 posterior end of the tricuspid membrane ; as soon as it is clear of the pylorus, it makes a double and plunges deeply into the body, nearly to the foot, through the folds of the liver, and then ascends to the dorsal region, to near the point from whence it commenced the circumvolution; it then proceeds under the peritoneum or membrane enveloping the liver and stomach to the pericardium, which it pierces, and passes in a straight line, embraced by the ventricle and auricles, to its termination in the anal tube. The Circulation and the Respiratory Organs. The circulation is complete; that is, there is an aortic action, and a venous reflux of the blood for aeration to the pulmonary apparatus. The respiration is effected by a pair of very long membranous narrow symmetrical laminae on each side of the body, composed of a vascular network, fixed under the mantle to the dorsal range, accompanied also on each side by a pair of palpi. On leaving the body the four branchiae without an intermediate substance run together tapering to their termination at about \ an inch from the extremity of the branchial orifice ; they are firmly fixed the whole length by their bases, from the point they leave the body to the membrane which separates the anal from the branchial cavity, cutting off all communication between the two siphons ; con- sequently the water must be received and ejected through the branchial siphon, or by the pedal orifice, in the bivalves with closed mantles, as is the case with the Pholades, and probably with other families of the same structure in which the branchial and anal tubes are separated their entire length by a divisional membrane. The discovery of this circumstance is so important as regards the disputed point, how the branchise receive the ambient element, that I have used every means to test it, by dissection, by all the modifications of experiment, and particularly by mercurial injections ; this last mode I have used very success- fully, as the following operations will show. First, I threw into the anal siphon a column of mercury that completely filled the cavity, and on applying further pressure, regurgita- 186 PHOLADID^E. tion ensued, but not a particle of the mineral found a passage to the branchial vault ; this result occurred in many specimens, and though the pressure was often considerable before regur- gitation was allowed to take place, still the branchial division of the mantle remained free from the quicksilver. In one experiment the fluid appeared in the lateral tissues; this I attribute to a lesion of the dorsal lateral membranes. 2ndly, I found that when there was not the slightest solution of continuity in the fine membrane on which the branchial vessels are fixed on one side, and the interweavings and traceries on the other, which form the roof of the anal siphon, the application of the mercury to that tube gradually filled the whole range of the branchial vessels, which exhibited a very elegant appearance, but no fluid escaped from them into the branchial sac. 3rdly, I repeated many times the first experiment with the view of endeavouring to find a passage through the rectum and intestine on the dorsal range that is embraced by the heart, but without success; if I had suc- ceeded, it would have been impossible to arrive at the stomach and mouth, as the intestine plunges into the body coasting the foot, at which point it is of larger diameter, and always filled with a compacted mass of sand which effectually stops up the passage : this part of the intestine around the foot, from its difficulty and the hardness of the faecal matters, seems analogous to the ascending portion of the colon in man. In all these attempts either regurgitation ensued, or the continual pressure of the mercurial column caused lesions. This impossibility to pass anything into the rectum pro- bably arises from its sphincter, or one in the anal tube, as the stoppage always occurred at that point where it empties into it. 4thly, On applying the mercury through the mouth and O3sophagus the stomach was readily filled ; but as soon as the pylorus was passed, a stoppage not to be removed occurred, from the duodenum being, like the colon in the last case, filled with sand ; we may therefore conclude that water can never enter the stomach of bivalves from the anal tube. PHOLAS. 187 The spaces lining the roof of the anal siphon consist of four longitudinal rows ; the two middle ones are the largest, and form transverse parallelogrammic figures, whilst the other two, one on each side, are smaller subquadrangular areas. I can conceive no other use for these crypts, in such families as have them, than as depositaries for the ova ; if so, the oviducts of course communicate with them, and the ova probably remain there some time after fecundation ; and the final ejection, in bivalves of this structure, can only take place from the anal tube. It is probable that the principal use of the anal conduit in the bivalves, in which the branchial cavity is completely cut off from the anal one, is to receive the rejectamenta, supply water to the ova during their maturation, and ulti- mately to eject them*. It is necessary to state that these experiments require much patience and attention, and some delicacy of manipulation, to arrive at sound results : it is very material not to use specimens with accidental lesions, or those made in removing the animal from the shell, which operation, from the obstruction of the crotchets, cannot be effected without some practice and dex- terity. The result of the 1st and 3rd experiments would appear to demonstrate the non-communication between the branchial and anal siphons in the Pholades ; this fact being established, they will not be the exceptions ; but it is probable that the Myadas, Solenidee, Lutrarice, &c. have a similar configuration of the branchial apparatus; and though the Veneres, Cardia, and other open-mantle bivalves have the character of their branchial sacs different from those of the Pholades, in not having the siphons completely separated, but more or less confluent, the possibility of branchial currents must be ad- mitted. Still, as it has been shown that in the Pholades the water cannot be received and discharged otherwise than through the branchial aperture, or from the pedal orifice, it * Since this was written, doubts have arisen whether the ova after exclusion are deposited for a time in the crypts of the anal tube, or in the branchiae ; we have never discovered any out of the ovarium. Exmouth, 1853. 188 PHOLADID^E. is clear that regular separate currents by cilia cannot exist between the two siphons, so as to make one the inhalant, and the other the exhalant canal ; and if there is any truth in analogy, every presumption authorizes us to conclude, that the same action of the reception and discharge of the water through the branchial siphon and pedal or ventral opening prevails in the open-mantle bivalves, the Veneres, Cardia, &c., wherein the brancliial sac is posteriorly divided into two, not separated, but confluent siphons at their bases, being only more or less divided towards their terminal portions by an internal septum, so that they must be considered in conjunc- tion, and as one siphon, for branchial purposes. If therefore it be established beyond all reasonable doubt, that there is no communication between the anal and branchial siphons in Pholas, there is an end to the doctrine of separate branchial currents by cilia; for if this is impossible in one family of the same class, we have a right analogically, and agreeably to the axiom " ex uno disce omnes/' to consider that all are in a similar category as to the mode of admission of the water to the branchiae, whatever may be the differences in certain classes in the disposition and structure of the siphonal apparatus. Having arrived at this conclusion, I will, though it is almost unnecessary in corroboration of it, make a few additional remarks. It is well known that muscles are often hung up high in the crevices of rocks, some of them above the level of the ordinary tides, where my dredger says that they remain suspended throughout the year, and can only for a few days in each month, at spring tides, receive the water : this con- dition may occur for about two hours in 75 days out of the 365 ; yet when any of these animals are opened, the cilia, under the microscope, will always be seen in action, beating, sub- dividing, and eliminating the air from the moisture. In this case, for near three-quarters of the year, the creation of branchial currents is impossible; they cannot be produced from nothing. It appears then, whether the cilia be within the possibility of assisting in the creation of branchial currents or not, their PHOLAS. 189 action never ceases whilst moisture remains in the shells, and I think it must be considered as settled, that there is no com- munity between the cilia and what are called branchial currents. I have at Exmouth repeated all the experiments with the mercury on fresh flexible animals ; the first were performed with rigid specimens from spirit ; the results are most satis- factory, and I think entitle me to state with confidence, that in Pholas there is no communication between the branchial and anal siphons. Since the above observations were written, I am enabled to state, after a prolonged and anxious examination of fifty living Pholades, under all the phases of experiment, that nine- tenths, if not all the water to bathe the branchiae is admitted at the pedal gape, and ejected only by the branchial siphon; the anal one alone inhales water and discharges it; and in the closed-mantle Solenidae, Myada, Lutrarice, &c., as well as in the open-mantle Veneres, Cardia, &c., the water is only admitted into the branchial vault at the pedal or ventral aperture by the simple opening of the valves, and ejected according to the structure of their respective sacs, either by the branchial issue alone, as in the Pholades, &c., or, as in the Veneres, Cardia, &c., by the two confluent orifices, which are in fact but one branchial conduit. This discovery and attendant results will finally, I hope, dispose of the complicated scheme of some authors, of the reception and discharge of the water for branchial purposes by cilia and separate siphonal ducts, as it shows what I have always advocated, that nature gives access to the water for the respiratory apparatus by the simple opening of the valves, and causes it to be discharged, when effete, by their closure at the posterior siphonal issue, as well as by the pedal opening and ventral scissions of the mantle. It is therefore I think satis- factorily proved, that the doctrine of separate currents by cilia, and that the inhalant is always kept distinct from the exhalant current and admitted by a separate aperture from that by which the latter is expelled, or in other words, that the water is imbibed by the branchial siphon and discharged from the anal, is absolutely untenable. 190 PHOLADIDJi. The important discovery I have just related was made manifest in the simplest manner. On taking up an animal, the siphons of which were largely inflated, I observed that the great mass of water was poured out from the branchial tube, and only a small quantity from the anal one ; on re- placing the animal in water, I was surprised, instead of seeing, as I expected, the water flow up the branchial canal, to observe a powerful column, through the tenuity of the membrane, pass rapidly from the pedal opening, in conse- quence of the relaxation of the mantle around the pedal gape, and fill the branchial vault. This very decisive proof how the water reaches the branchiae induced me to vary the experiment. I placed the animal with the tubes entirely in the water, and the pedal gape out of it ; very little fluid entered the branchial sac, the anal siphon alone imbibed a portion ; and on holding the animal with the siphons downward, scarcely any water issued from the branchial one, and only a little from the anal ; but as soon as I suffered the pedal gape to reach the water, a column was instantly seen to fill it as before. I do not mean to say that if the pedal aperture is kept out of the water, some fluid may not be imbibed by the branchial tube ; nature will supply its wants by other channels if de- prived of the accustomed ones. I only insist on the position that the usual canal for the entry of the main body of water for the use of the branchiae in all bivalves is by the pedal and ventral apertures ; that the exit is by both the branchial and pedal fissures of the mantle ; that these actions are ac- complished agreeably to the wants and will of the animal at uncertain intervals by the simple opening and closure of the valves, and that what are called currents by cilia do not exist. I cannot help again observing on this simple solution of a disputed point ; I may call it as simple a one as that of Columbus, when he showed how the egg may be made to stand on its apices ; and yet it is quite decisive of the desired point, how the water is admitted to the branchiae. The Secretory Organs^. Under this head, as I propose to offer at a future time some PHOLAS. 191 observations on the anatomy of the Lamellibranchiata, I will only at present mention the veins and glands which I think produce the cartilage and ligament. On carefully opening the lateral cavities on each side the anterior dorsal range, a fasci- culus of veins may be seen deposited therein, some of which I have traced to the liver ; and it is probable that the inspissated fluid thrown oft* by them is specially applicable to the formation of the cartilage and internal portion of the ligament, as I have found their excretory ducts to be spongy masses that send forth the viscous humour distilled from the veins on the in- ternal convex circular areas in which the valves articulate ; and a proof of one at least of the true uses of the excretory apparatus is, that in Pholas dactylus the fluid is of a light brown or drab, and it produces two thin cartilaginous plates of those colours, whilst in P. parva the colour is as dark as tar, and the plates of the cartilage correspond with it. It is probable the coarser parts of this secretion are separated from the concentrated cartilaginous matter, and form the interior layers of the ligament, the mantle only producing the external skin. It is reasonable to suppose that all bivalves have these secreting organs; and it will be desirable to ascertain if such shells as the Mactrce, Myee, Lutraria, &c., which have internal cartilages of considerable volume, have the excretory and secretory organs correspondently developed as in the Pholades ; and if in those genera that have external cartilages, there is any variation of structure. TJie Reproductive Organs. The Acephala are hermaphrodites without congression, and as it is termed, they suffice for themselves ; but this fact must not be understood ideally, as these animals have distinct visible organs, the union of which, within themselves, produces the male and female influences. I hesitate to concur in the state- ment of some authors, that the sexes are distinct in the bivalves. I think it is probable that this idea has arisen from the animals being examined at different periods of the year. In the genial months, the ovaria, and the virile membranous pouches, are distended and fully developed ; but in the winter 192 PHOLADIDjE. season, when all nature flags, and takes repose after the exhaustions of the summer, and when even the influences of the "^Eneadum Genetrix" are softened down, then the ovaria and the pyriform virile membranes become obsolete : these two very different states may have contributed to pro- duce erroneous conclusions. We must, as I have elsewhere observed, not forget the precept, " .ZEtheris et terrse geuitabile quserere tempus." I do not mention that I have quoted this line a second time, as an apology for the repetition ; on the contrary, I mean to mark the great importance in which it was held by the illus- trious author, who has in his work repeatedly used it or its equivalent. The ovarium of P. dactylus is a conical organ, amalgamated with the lower part of the body, having a pointed apex. Though I applied the quicksilver, I did not satisfactorily make out the oviducts ; they do not appear to be at the apex of the ovarium, and I am inclined to think that they are situate at the junction of the body with that organ. In many bivalves it is considered that the ova, on issuing from their receptacles, are at once committed to the protection of nature. This idea is mainly correct, but in certain species, for example in the Kelliada, &c., the ova, after fecundation and exclusion from the ovarium, are for some time committed to the protection of the parent before final ejection; in Anodon and the Mytili, they are transferred to the branchial laminae for maturation. In the Pholades, we believe the ova pass at once from the ovarium into their native element. Since the above observations were written, Messrs. Alder and Hancock have dissented from my theory ; I replied by the following letter : To the Editors of the Annals of Natural History. GENTLEMEN, Exmouth, September 1853. I request permission to reply to Messrs. Alder and Han- cock's comments in the ' Annals of Natural History/ vol. viii. PHOLAS. H3 p. 370. pi. 15. N. S., on my branchial theory, which appeared in a paper on the Pholadida in vol. vi. p. 313 of that publi- cation. I was so engaged last year in the examination of a splendid harvest of rare animals, that I had no time to con- sider their remarks, but having now an unlimited supply of Pholades, I will endeavour to acquit myself of my engage- ments with these gentlemen. They commence by quoting parts of my theory, and say that I announce " that T %ths, if not all, the branchial water is admitted by the pedal gape." On this point they observe " Let us for a moment consider what would be the conse- quence of Mr. Clark's supposition, that these animals obtain water only by the pedal gape. Nearly all of them pass their lives buried in sand or mud, or immured in solid stone, with only a small aperture externally, the pedal opening being be- neath, and the siphonal tubes in communication with the sea. Yet Mr. Clark would have these animals receive only the small quantity of water charged with sand and mud that finds its way to the bottom of the cavity, rather than draw their supply from the pure element on the surface, by means of their long siphons." To this quotation I reply, that a fresh and very extended examination of four species of the Pholades fully supports me in maintaining all my positions, and I think I shall demon- strate that Messrs. Alder and Hancock's system of branchial currents is erroneous. The only correction I have to make is, that I have clearly ascertained that the branchial, like the anal siphon, is both inhalant and exhalant. With respect to their observations on the habits of the Pholades, it is only necessary to admit, that these animals often inhabit sand and shingle, mixed with clay, and are not always imbedded in hard rock. But we contend that the cavities in Avhich they dwell afford sufficient passage for the sea- water, and the areas of their habitats are saturated there- with, as when the tide withdraws, much of its waters is retained by the various strata, which by filtration reaches the burrows in a pure state, and not "charged with sand and mud." o 194 PHOLADID^E. Continual watchings for months of multitudes of these ani- mals prove beyond doubt that the water is not only copiously received at the pedal gape or aperture, but is often expelled with as much force, and with a similar formed jet, as from the branchial siphon ; and my dredger, who during the last fifty years has excavated more Pholades than any man in existence, says, that he continually sees the water expelled from the pedal gape. This is an important fact in corroboration of my theory, as an in- and ex-current is established pedally in combination with the branchial siphon. I will now mention a decisive proof that nature, in all the bivalves, intends the water, under certain conditions, to be received and expelled by the pedal gape or aperture. When the gape of the Pholas papyracea is closed, by being domed by the animal, a large ovally dilatable fissure is always left for the water in the connecting membrane of the laminae of the dome, in its centre, to correspond with the gape that has been rendered ineffective. And in the linear Soleus, in which, from the quality of the foot and its singular position, the water cannot well enter pedally, a similar aperture is also left in the membrane of the connecting valves. In the Mycz and other bivalves the water has access through the ventral and pedal apertures. Thus we learn from these examples that when nature has denied the ordinary pedal entry and exit for the fluid, she always supplies a compensation. The periodic entry and reflux of the branchial water present two distinct characters ; the one being regular, the other more uncertain. With respect to the first, place a dozen Pholades and as many Pullastra puHastra, or P. decussata, in a dish of sea-water : it will be seen that each has a regular periodic action, the Veneres usually from one to two minutes, and the Pholades three to four, until a change of circumstances in- duces a new disposition. The entry and issue of the fluid, in conjunction with the pedal gape and aperture, are thus per- formed : the animal simultaneously closes the orifices of both siphons, which after a short pause are again opened ; the effete water flows from both, and fresh is received. But independent of these silent though very visible operations, there is about PHOLAS. 195 every five minutes a powerful and copious jet from both tubes, sometimes simultaneously, at others at intervals, and that from the branchial tube in the Pholades is almost always accompanied by a strong ejection from the pedal gape, and also in the Veneres from the pedal aperture, though from the absence of a gape in their shells it is not so visible. The periodic times of the in- and out-flux, of whichever character it may be, as the animal becomes exhausted, are more and more prolonged ; they are only in vigour for twelve hours. What is the object of these copious and regular receptions and expulsions of water ? Will not every reasonable person acknowledge that they can only serve for branchial purposes the receptions, to administer water to the gill-laminse, and the expulsions to remove it when effete by the contraction of the adductors of the valves and siphonal retractors ? In cor- roboration of the above, I particularly refer to the Rev. James Bulwer's account of the Isocardia cor, published in the 'Zoological Journal/ vol. ii. p. 258. Messrs. Alder and Hancock cannot controvert these facts, and therefore in rela- tion to my theory say, "This is, however, a special case having nothing to do with the regular branchial currents, as has before been pointed out to Mr. Clark." My opponents may find their special case a general law, and their system of regular branchial currents an illusion. They, having discovered that no ascertained communication [this is a condition of my theory] existed between the branchial and anal chambers, thus express the fact : " We certainly find no opening between the foot and the gills, nor between the gills and the mantle ;" and in consequence of their favourite doctrine being in jeopardy, they "found it necessary to make a careful examination of the anatomical structure of these animals," and have informed us of the discovery of a channel, by declaring the gill-lamiuse and their interbranchial tubes permeable, on which to them a most important fact, if true they emphatically observe, " Thus in an instant the secret was explained ; the currents commu- nicate through minute openings in the laminae of the gill- plates." o 2 !!)<> I think these gentlemen have formed an erroneous con- clusion : I cannot accord with the monstrous position that the impure branchial water, deprived of its oxygen by the cilia, and of the alimentary matters by the palpi of the animal, is sent by nitration, even if pores existed, through the gill-laminse and interbranchial tiibes, which are the sup- ports of the delicate blood-vessels for discharge at the anal siphon. As the capacity of the branchial chamber is at least three times greater than the anal, Messrs. Alder and Hancock must admit that two-thirds of its fluid is expelled agreeably to my theory ; it is therefore difficult to conceive a plausible reason why a part of the effete water, only one-third, should be got rid of by an issue, termed by them a branchial current. The sustentation and aeration being unquestionably effected in the branchial vault, we may inquire, what is the object of this partial labyrinthine exit for the water instead of its being wholly ejected by the pedal aperture and branchial siphon, at which it entered, agreeably to the simple laws of nature ? In connection with these views, I state a fact that may have some weight even with the sceptical. The longitudinal retractors and transverse muscles of the siphons are of very great power ; the office of the latter is to diminish the calibre of the tubes, that, in conjunction with the former, they may effect a more powerful expulsion of the impure fluid. As proof, if a dozen Pholas dactylus are placed in a large dish of sea- water, they will cause so great an ejection from the siphons, not from the effect of sudden disturbance or being startled, but of regular periodical emissions, as to cover the table several times during the twelve hours of the day and also throughout the quietude of the night : assuredly this circumstance serves to prove that the impure water is thus expelled, and that no part of it permeates the interbranchial tubes. However, it still appears that Messrs. Alder and Hancock insist on a regular in-current by the branchial siphon, and an ex-current from the anal, effected by cilia, for the use of the respiratory apparatus ; these are, as I think, strange and PHOLAS. 197 impotent motor agents. I have in a former paper expressed a belief that the function of the cilia is to beat and subdivide the water, that the oxygen may be the more easily extracted. I must now observe that all the testaceous Mollusca have many parts of their bodies clothed with cilia, which show their action in a similar manner to the Bivalves. What then, in them, are the functions of these appendages ? May we not reason- ably conclude, the same as in the Bivalves, to extract air from the water not only for their branchise, but perhaps to pass the vital fluid through the pores of the body. One can hardly suppose that in either group their duty is mechanically to create currents, when a more simple, visible, and effective plan exists ; I therefore think the view is untenable, that they effect the in- and out-flux of water in the anal and branchial chambers. I believe a simple hydrostatic law provides for this operation in all the Bivalves by a vacuum being formed by the contraction of the valves in the expulsion of the effete water, and that on opening them and relaxing the siphonal orifices to take in a fresh supply the vacuum ceases. The action of the cilia is local. That they produce currents or rather eddies on the gill-laminae and different parts of the body of the Gasteropoda cannot be doubted ; these result from every stroke of each that causes a displacement of fluid which instantly reverts to its level, but they are not the locomotive agents of the entrance or exit of the branchial water ; they are strictly particular, having no determinate line of opera- tion, and act indiscriminately from every pole. As presump- tive proof, examine an oyster or a muscle from a provincial stall a few days after they are received, when the cilia under the microscope will be found in full action as if just taken from the sea, and will continue so as long as moisture re- mains. In this case these species, even if they had siphons, could not produce in- and out-currents by separate ducts, from non-access to Avater; we are, therefore, bound to give the preference to the idea that their functions are to eliminate the oxygen. I may observe, that cilia are attached to the different epithelia in all animals, from the monad to man. The inconsistency of such a motive power will be apparent 198 PHOLADID.E. from the consideration that the cilia must act antagonistically from opposite points; one set to work the water in bran- chially, and another to expel it through the anal duct after percolating the gill-laminae and interbranchial tubes. I shall recur to the cilia, and expect to prove that the new scheme of communication between the two siphons is very problematical, I may say impracticable. Messrs. Alder and Hancock go on to say, that any one may convince himself of the existence of a branchial in-current and an anal ex-current, by placing a Pholas " in a glass of sea- water, and then by gently adding a little fresh, slightly charged with floating particles," the two actions may be per- ceived. I admit, by this process, that currents will ensue, as the invigorating fresh element causes the animal to expel that which has become effete and take in a new supply ; but as I have, under every condition of experiment, examined multi- tudes of these creatures, I am bound to declare that the currents have no continuous regularity : and I think the mode of testing their presence by means of water charged with buoyant particles is fallacious ; these only float on the sur- face, and are subject to many perturbations and deceptions arising from depth of water, currents of air, the position of the animal, whether on the ventral or dorsal surface, by its will and humour, state of exhaustion, and an unnatural con- finement. My repeated examinations show that the parti- cles are whirled in all directions ; sometimes they pass into the branchial chamber, at others none will enter : capricious gyrations, whether arising from the action of the animal or other natural causes, are their ruling character. With respect to the anal siphon, the floating particles are certainly repelled from its orifice in a somewhat regular and continuous manner, being only interrupted by the periodic reception of fluid to supply the exhaustions. The frequent repulsions of particles from the anal orifice have been construed by Messrs. Alder and Hancock to arise from the percolation of water from the branchial vault through the gill-laminae and interbranchial tubes to an issue at the anal siphon, produced by the agency of cilia. I think it will appear that this complicated operation PHOLAS. 199 will meet with insurmountable difficulties., and though I admit the anal outflow, I protest against its being considered of branchial origin and regular; the regularity is fallacious, though most naturalists appear to have adopted that idea, without perhaps sufficient examination, and others have been careless in their observations. But the diligent observer of cause and effect will perceive that there is as much water inhaled as expelled by the anal siphon, and that its fluctuation in the branchial chamber, produced by the contraction and dilatation of the four gill-plates, which can often be seen by a lens through the orifice of a large P. dactijlus, aided by the respiratory circulation, causes a pressure and an impulse on the interbranchial tubes; these, as before shown, are filled every two to four minutes by a reception of water anally, which after performing its function, of whatever nature it may be, is thus for a similar period made to reflow into the anal cavity, and from thence is discharged by an insensible con- traction of the siphonal muscles until the exhaustion of the fluid : this is very evident by the failure of the current, which only recovers its full action on the periodic renewal of the water. I have thus, perhaps, explained the mystery of the so-called branchial current, It is problematical what are the precise functions of the water that is received into the interbranchial tubes and anal vault ; I have hereafter alluded to some of them conjecturally, and for the present will only observe, that as this tube acts as a conduit to the contents of the rectum, one probable use of the water is to break down and remove the dejections ; and it would indeed be strange if it had no other entry, except from the branchial vault by the devious route of filtration through the interbranchial canals. In further support of the view that the anal ex-current is not the effect of a percolation of liquid through the gill- laminoe, I will for a moment digress, and relate a short inci- dental experiment. As' the anal siphon is somewhat longer than the branchial, it is easy to subject the latter to the in- fluence of the water and isolate the former; it resulted, that whilst the water flowed into the branchial cavity, none, in an 200 PHOLADID.E. hour's constant observation under the lens, issued from the anal siphon, a sufficient proof of the non-communication of the two ; but as soon as the anal siphon was allowed to reach the water and obtain a supply, the current recommenced. I now come to another experiment from which Messrs. Alder and Hancock conclusively infer the connection of the w siphoiial currents. They state, " that the iiosle of a blowpipe charged with a coloured fluid was placed at the inhalant orifice of a Pholas, and immediately a quantity was drawn into the animal. Watching carefully the result, we had soon the satisfaction of beholding a blue-stained stream issue from the exhalant orifice." To this I observe, that having tried the experiment again and again, failure always occurred ; as the animal, after re- ceiving the coloured fluid, which was applied without difficulty, in general immediately discharged it by the pedal gape, or by the branchial aperture overwhelming with coloured matter both tubes, the orifices of which, from their inflection by the animal, were so retracted and blended together as to be undis- coverable ; of course, any issue of liquid from a particular tube was undistiiiguishable. When, in any example, the fluid, which was coloured by archil, remained a little time without expulsion, I opened the branchial cavity to see if the gill- laminse and interbranchial tubes showed anv increased infla- v tion or colour from the filtration of the injection, but no unusual appearance presented itself. I also opened the anal vault and collected with a camel's-hair brush as much of the moisture as possible ; this was applied to a very small quantity of distilled water, but no trace of colour appeared ; we may then presume that none of the injection had passed from one siphon to the other. But when the coloured fluid was ad- ministered anally, all the interbranchial tubes were at once filled and remained inflated more than an hour, representing minute well-filled hoses, which bore the pressure of a delicate wooden stylet, and exhibited the fluctuations of the liquid, which, on its removal, instantly reverted to the points of dis- placement, without any escape into the branchial chamber. We may therefore conclude, that the interbranchial tubes are PHOLAS. 201 impervious tissues, and are supplied through the orifices of the crypts from the water sucked in by the anal siphon ; and one of their uses is probably, by being filled, to afford a sufficient tension to the network of the blood-vessels that they may the better receive the action of the cilia : they may also possibly be the receptacles for the maturation of the ova, agreeably to the opinions of some naturalists ; but in the multitudes I have examined I cannot corroborate this view, as during the months of May, June and July I failed to see any deposit of ova either on the gill-laminae, or within the interlaminar cavities, or in the crypts of the anal vault ; still the " genitabile tempus" may be later ; nevertheless the ovaria were well filled with germs of various sizes. Under all the circumstances of this experiment, I think, though it may not be impracticable, that it cannot be depended on even if the gill-laminae are per- meable ; but as I confidently believe no communication exists through them, I must conclude that these gentlemen were mistaken in supposing they had detected an issue of coloured fluid from the branchial vault through their exhalant siphon. I have now to consider the principal experiment, which Messrs. Alder and Hancock think will settle the disputed problem of in- and ex-currents in the Bivalves, produced by the action of cilia through separate siphons. They say, " But a simple experiment will at once solve this difficulty. Having killed a specimen of Pholas crispata with the siphonal tubes contracted as little as possible, and having placed it in diluted spirit a few hours to render the tissues firm without hardening them too much, we had again recourse to the blow- pipe, charged as formerly with coloured fluid. The specimen was opened down the ventral margin, exposing to view the whole of the gills stretched along the roof of the branchial cavity. The nosle of the blowpipe was passed into the anal siphon, and on removing the finger from the top of the pipe, the contained fluid immediately filled the anal chamber behind the gills, and then passing at once down the tubes between the laminae of the gills, issued through ten thousand pores, and dyed the water in the branchial chamber. Thus in an instant the secret was explained; the currents com- 202 PHOLADID.E. municate through minute openings in the laminse of the gill-plates. " Having thus satisfied ourselves of this fact, we next directed our attention to the structure of the gills. Accordingly, the anal chamber was laid open, and its ventral wall was seen to exhibit four longitudinal rows of large orifices. These four rows of orifices, already well known to anatomists, correspond to the attached margins of the four gill-plates, which hang from the roof or dorsal membrane of the branchial chamber ; this membrane being the ventral wall of the anal chamber, the membrane, in fact, which divides the chambers. " These orifices lead into wide tubes which pass between the two laminte forming each gill-plate. These interbranchial tubes lie contiguous and parallel to each other, and extend the full width of the gill, being bifid within its free margin. Thus it is evident that the tubes within the gill-plates com- municate freely with the anal chamber. The laminae forming the walls of these tubes were now examined through the mi- croscope, when the whole was observed to present a regularly reticulated structure composed of blood-vessels ; those passing transversely being the stronger and more prominent. The longitudinal vessels, rather far apart from each other, form the meshes into parallelograms. These meshes are open spaces, fringed internally with a narrow membrane and active vibratile cilia. The two vascular laminae forming the gill- plate are really sieves to separate suspended molecules from the surrounding medium on the passage of the water from the branchial to the anal chamber; an apparatus of the most exquisite beauty and perfect adaptation to the de- sired end. " We cannot understand how this beautiful structure escaped detection by the mercurial injection of Mr. Clark." I at once dispose of the last remark to save trouble in my counter-statement. If these gentlemen had read a little more attentively, they would have seen, in the paper on which they have passed their strictures, that Mr. Clark states, " The appli- cation of the mercury to that tube gradually filled the entire range of the branchial vessels, which exhibited a very elegant PHOLAS. 203 appearance, but no fluid escaped from them into the branchial It is proper to state, that the Pholas crispata is the species that has furnished my controversialists with their remarks on .my branchial theory, which is illustrated chiefly by the P. dac- tylus. I am not aware that this circumstance is of much moment, as we may safely conclude that the gills of all the Pholades have in essentials the same character. But I ought to mention, that the framework of the respiratory apparatus in some tribes of the Bivalves presents a very different ar- rangement. For example, there are several British families, whose species I have seen alive, and which fortunately can be obtained, that have a peculiar branchial construction, which appears as to general configuration closely analogous to that lately described in the 'Annals' to exist in the Chamostrea albida and Myochama anomioides of authors, but the particular parts of the mechanism in my species do not accord ; I think the narrow reticulated ribands on the external surface are not permeable, and do not lie on apertures that communi- cate with the interbranchial tubes. I refrain, at present, from extending these remarks ; but I shall be prepared with some comparative notes on certain species that have only a single complete gill-lamina and a rudimentary one on each side of the body, Avhich seem to me to differ essentially in structure from the descriptions that have been promulgated on the composition of the branchial mechanism of the species that have been alluded to. I now enter on the counter-statement to the last quotation, and beg to observe, that Messrs. Alder and Hancock, in the explanatory sketch of their Pholas crispata, 'Annals,' pi. 15, vol. viii. N.S., give a very intelligible outline of their theory. Though entirely dissenting from it, I cannot but admire the ingenious delineation, particularly fig. 3, of the gill-laminae, showing the aspect of the meshes ; it has, however, one fault it exhibits them all with symmetrical longitudinal fissures called " orifices/' which I think are ruptures of the mem- brane of each mesh, not one of which exists naturally in the three species I have examined. 204 PHOLADID^E. Since May 1853 I have often performed "the simple ex- periment" detailed by Messrs. Alder and Hancock in the third paragraph of their paper, p. 374 ; it is by far the most im- portant of the series, as the problem of communication, with them, between the anal and branchial siphons, depends on it. By the injections of more than 200 Pholades with mercury and coloured fluids, the invariable result has been my inability, as in the first experiments in 1850, to pass the fluids through the anal chamber further than to fill all the iiiterbranchial tubes ; but I always found the gill-laminae, which form their walls, impervious, instead of allowing liquid to issue "from 10,000 pores." It is necessary to state that the numerous inteiiammar canals that compose the divisions of the gill- plates are nearly parallel, and hang vertically from the dorsal line, ranging at equidistances throughout a great part of the extent of each branchial plate, and by sutural lines of junction cut off the communication between each tube. I will now enter a little more into detail on some points in connection with the branchial laminae, by describing the ap- pearance of the areas of the parallelograms under repeated examinations by transmitted light, and also as opake objects, rendered so by the injection of mercury. In a full-grown Pholas dactylus, the surfaces of each gill- lamina together comprise an extent of about a square inch, every one-tenth of which contains 400 oblong subquadrangular spaces, or 40,000 in each plate, forming a total in the four gills of 160,000 ; this admeasurement and enumeration may not be very far from the truth. In each parallelogram, besides a general suboval depression, there are within it from five to twenty or more shallow excavations of various size and shape, but there is no ruling symmetrical fissure as delineated in Messrs. Alder and Hancock's fig. 3. Each area shows a plain, a pitted, and a mammillated or traceriecl surface, detected by the action of the microscopic foci. We will start from the plain surface, in which there is certainly no perforation : the fine adjustment of the instrument measures the depth of the depressions, and by another movement shows the character of the minute points, thus proving that no fissure or aperture PHOLAS. 203 exists ; as when there is really an imperfection in the mem- brane it cannot thus be resolved, but under every phase of the instrument the hiatus of a solution of continuity is seen. The shallow depressions are the uncovered patches of the mem- branous base of the scales or epithelium, incident to all the Mollusca ; from them the numerous vibratile cilia spring, which present the most discordant and particular motions that operate from every point ; sometimes they appear as if each entire pit was whirled on a vertical axis, at others a compact mass of strands dilates and contracts like the heart, then a fasciculus of cilia is seen beating the water with irregularity ; some- times only a single cirrhus is raised in quick succession, like a hammer in a mechanic's hand; but it is impossible to describe all the varieties of motion. In a fresh animal, the action and strokes exhibit the greatest rapidity ; it seems utterly impracticable that regular currents can be formed by such a chaos of agency ; rapidity and diversity is the natural character of the action of the cilia, and it is only by the ex- haustion of moisture, which can never occur in natural sites, that a subdued and more deliberate motion is attained, and even then their direction is as variable as ever ; I can only consider them as the eliminating mechanism of the oxygen. The epithelium is pretty regularly deposited on the upper area of a compound membrane, one lamina being thin, horny, and of a pale yellowish brown ; the other thicker, of a more mucous quality and whiter colour : this is seen by examining the edges of a section. Between those membranes which form the sub- stance of the gill-plates the network of the blood-vessels is spread, as without such support it would fall to pieces : per- haps the roots of the cilia pass through the epithelium and its supporting membrane, and impinging or centring on the coats of the blood-vessels, by a capillary or porous action supply them with the air they extract from the water. It is scarcely possible to view a more interesting object than the structure of the branchial mechanism and operation of the cilia, by trans- mitted light, under a power of 300 or 400 diameters. I think these data will almost convince naturalists that these organs 206 PHOLADID^E. cannot be the agents of a communication from the branchial chamber to the anal siphon. It is necessary to state that occasional lesions, and now and then a perforation, are seen on the surface of the gill-laminse, the evident effect of a casual imperfection ; Avith these excep- tions, entirety is the ruling aspect; all my fellow-observers concurred in this opinion; and two pieces of gill-lamina containing several interbranchial tubes were submitted to a distinguished metropolitan microscopist, who thus reported on them : " I can find no pores in them, unless a piece of leather may be called porous." Since this opinion a great number of the gill-membranes of the Pholas dactylus have been examined by transmitted light by one of Mr. Ross's microscopes, with the ^ and of an inch object-glasses, a power more than sufficient to detect the presence of natural symmetrical apertures or pores through which effective per- meation could be obtained ; indeed that power would be equal to show pores through which no water could pass freely, and scarcely by exudation. The gill-plates of the Pholas parva are more delicate than in the ( dactylus.' No appearance of symmetrical apertures exists, but only an excessively minute wiry traceiy, studded in the interstices with points, which, under a power of 300 linear, only presented a surface little larger than the point of the finest needle, and had the aspect of prominent dots rather than pores. In the Pholas papyracea the gills are of the finest texture, but exhibit no appearance of a permeable structiu'e ; minute points are scattered in the traceiy of the parallelograms, some of them being circled by a shallow grooved line ; but this is merely a depression of the epithelium or its supporting mem- brane. I have preserved the preparations. Having mentioned accidental lesions and gill-laminar im- perfections, I have to add, that in testing Messrs. Alder and Hancock's chief experiment, no alcoholic injections should be used, as by their penetrating quality they may exude through these super-eminently delicate tissues ; nor should mercury be PHOLAS. 207 employed, as its weight iu young subjects without great care often causes ruptures, and from its density it does not pass so freely as aqiieous fluids. Sea- water coloured by indigo or archil, or pure, is the proper injection, which must not be pushed beyond a full distension of the interlamiuar tubes. The animal should be prepared in as natural a state as possible, and not be killed by any process producing sudden asphyxia, as immersion in hot water or alcohol ; the first destroys tenacity in delicate tissues ; the second thickens and hardens them too much, and occasions lesions and fissures by contraction. There must be no lesions in the gill-laminae, except those that result from imperfections, which prevail to more or less extent in every animal I have examined at least 500 ; any solution of continuity at the junction of the gills with the excessively delicate membranes of the body will be fatal to success. If the experiment is thus conducted, no injection through the anal siphon will flow into the branchial vault by the route of the interlaminar canals ; the only moisture, if any, that can arrive there, may be a slight exudation, a proportionate one to the number of perforations and cracks in the membrane from laminar malformation, and of these only those which pass through into the interbranchial tubes. There may be in the 40,000 parallelograms in each gill, about twenty flaws or imperfections, and I reserve the possibility that all or most of these may arise from the manipulation of such delicate tissues. After all these incidents, how am I to explain the great discrepancy between the experiments of the northern na- turalists, illustrated by their " 10,000 pores," and mine, from the impossibility of causing fluids to issue from the inter- branchial tubes by percolation through the membrane on which the network of the blood-vessels is spread ? But 'tis said, the sight is keener in the North than with us southrons. The only solution I can offer is a mere guess, that the animals operated on by these gentlemen, after being killed, and alcoholized to harden the fabric, and the contractive qualities of alcohol are well known, had, when the moisture was 208 PHOLADID.E. evaporated, the membrane of the entire network of the branchial laminae broken by lesions and contractions ; and their fig. 3. in the plate has much the aspect of such ruptures. " I cast this idea on the waters/' as Southey did " his little book/ 3 and it may have as much value as it deserves. I had scarcely written these lines when I found that my conjecture might be right. Having opened in a gill-plate an inter- branchial tube that retained the injected mercury, I cleared it of the mineral, and being dry it was placed in water to recover pliability, for fixing on a tablet, on which it was care- fully spread without stretching; I found that in the central portion of the membrane of the plate almost every parallelo- gram was ruptured, which under the microscope showed no previous solutions of continuity, and each fissure proved a fac-simile of those delineated in the ' Annals/ vol. viii. N. S. pi. 15. fig. 3. The area of the portion of the gill-plate examined contained about 2000 parallelograms in rows, and by its size caused the sphere of contractibility to centre in the middle, whilst towards the margins, a less resistance and greater elasticity prevailing, many of the rows of network preserved their integrity. I then prepared another portion of ten transverse and as many longitudinal rows ; in this diminished area not a mesh was ruptured, and the membrane of the blood-vessels remained perfect. It appears then, that the moistening of the gill- plate with fresh water and of course with alcohol a much greater effect is produced may have caused all the fissures in Messrs. Alder and Hancock's specimens, thus fully accounting for the singularly different results of our respective injections of the anal siphon. If I am right in these points, the question of in- and ex- currents by cilia and separate siphons is disposed of. The data of these gentlemen to show a communication between the anal and branchial vaults through the membrane of the network of the gill-laminae not being tenable, of course their theory falls to the ground, on the principle of " sublata causa, tollitur effectus/' consequently mine, as published in the 'Annals/ 1850, has not yet been proved incorrect. PHOLAS. 209 Hitherto the Pholades have been more particularly the object of consideration ; it may now be not amiss to turn our attention to a group of Bivalves which, though essentially the same, differ materially in the configuration and arrangement of many of their organs ; they may perhaps assist us in searching out the truth, by the discordancy of their attributes with those of their precursors. What view am I to take of the Anomia and Ostrece, that have open mantles and no tubes ; in which the water must enter at every point of the periphery that is patent, contemporaneously with the opening of the shell by the animal ? Here the water cannot be passed off by what is called an anal tube, because none exists ; it must therefore be discharged by the great ven- tral cavity. Am I to idealize, and suppose that in the same branchial vault there is a distinct current of ingress and an- other of egress ? I may observe, that in the Gasteropoda there is a similar periodic entry and expulsion of water from the branchial chamber as in the Bivalves ; and after the cilia have extracted the oxygen, I have witnessed a hundred times the forcible expulsion of the effete fluid by a jet as decided as in them ; am I here also to suppose that there are two distinct opposite currents in the same undivided cavity ? I have now to inquire how the gill-percolation, admitting for argument that it exists, is disposed of in this tribe of Bivalves without siphons. If the water permeates the gills of the Pholades, it must do so in the Anomice and Ostrece ; in the former there is a possible vent by the siphon, but none in the latter, therefore it must revert to its source, the branchial cavity. Does not this go far to prove that there is no per- meation in either case ? Then, may it not be permitted us, in this asiphonal group, without having recourse to an " olla podrida," or hash of cm-rents, to conclude, that when the animal opens the shell for the admission of water to bathe the branchiae, and when that function is accomplished, it ejects the effete fluid by the same channel it entered, as no separate duct can be found ? Will not the calm consideration of this case make most men doubt the existence of branchial currents either by distinct 210 PHOLADID.E. tubes, that is one inhalant and branchial and another ex- halant and anal, or by what I term supposititious ones ? The former position I think I have proved in the Pholades, by showing that there is no effective communication between the two chambers ; and in the Anomice and Ostrece, that the latter condition of the currents is imaginary, appears to be the most correct view. It may therefore be considered that in the Bivalves, whatever -modification their siphonal mechanism may present, all are subject to a general law of the water being expelled from the same siphon or channel at which it entered, aided by the pedal gape and pedal aperture where they exist; and in the Anomice and Ostrete, in wliich these organs are rudimentary or entirely wanting, the water is simply received and expelled through the ventral range, and not by an imaginative inhalant and exhalant regular current, effected by cilia. The remainder of Messrs. Alder and Hancock's paper re- quires no further notice except a few words on their concluding experiment showing how the colouring matters collect in the neighbourhood of the buccal aperture. I have observed these appearances, but I am of opinion, that in an animal cut up from stem to stern, with the so-called in-current, as they admit, annihilated, little dependence can be placed on the action of the gill-laminse floated in a shallow vessel, to account for the colouring matters seen at its oral termination. And I cannot understand the hydro-pneumatic statics of these gentlemen, nor the position agreeably to their theory, that " a tendency to form a vacuum " in the anal chamber and interbranchial tubes is effected by the " flowing out " of the water from the ex-current siphon, combined with ciliary agency, which actions, they add, are the foundation of their " correct answer to this question : How is the matter, divided into such minute particles, collected on the surface of the gills?" But a fallacy with respect to a tendency to form a vacuum seems to present itself, as in this case a flowing out involves the idea of a flowing in, which militates against the vacuum, for the fact is, that with the outflow there is in their theory a PHOLAS. 211 contemporaneous succession of fluid to compensate any pos- sible exhaustion. One would rather suppose that a tendency to a vacuum, instead of existing in the anal chamber, the point of issue, would be formed in the branchial vault, the source of supply, from a possible deficiency of fluid : a river shows no appearance of vacuity at its debouchure or elsewhere, whilst its sources maintain their integrity. I can conceive in a running stream that the pressure of one portion of water on another produces an impulsion, not a vacuum ; but how is this impulsion from, mere declivity of gradient to operate in the Bivalves, in which the natural position of the siphons is almost invariably at an angle of 90 in reference to the horizon ? How is the flow out of water to be effected in them ? Are we called on to believe that the cilia, besides eliminating the oxygen for the blood, perform the function of a pumping apparatus? Surely I need not further entertain such an absurdity; we may therefore con- clude that the water is expelled at intervals of two to five minutes from both chambers, by the powerful adductor muscles in combination with the siphonal retractors of the animal operating on the valves ; these agents act as a force- pump ; there is no other adequate exhausting mechanism. I do not think the idea of ciliary currents, independent of those for the extraction of the oxygen, can be sustained. I also cannot admit, with my views of the impermeability of the gill-laminae, that the concluding hypothesis of these gen- tlemen throws " some light on the sustentation of the Lamel- libranchiate mollusks;" I believe the gills are strictly a respiratory machine, with the exception that they may be subservient in some or all the Bivalves to reproduction. I consider that the palpi are the purveyors and locomotive agents of the alimentary matters. As a last argument I submit a syllogism, which perhaps some of your readers will say, from its decisive character, had better have been placed at the head, instead of the end of this paper, and thus they and myself would have escaped the trouble of wading through long accounts of optical and other experimental tests. p 2 212 PHOLADHLE. In a gill-membrane in which cilia are planted, epithelium is always present, and it and its supporting tissue cannot exist without a membranous and mucous substratum ; these are absolutely antagonistic to water, and impermeable ; there- fore the gill-laminae of the Pholades and other bivalves are impermeable. I apprehend, that ciliated mucous membranes are neither absorbents nor emuuctories, though the vessels of such glands may pass through them to the surface ; they are probably a product by exudation from the blood-vessels, for the formation of an upper membrane and the epithelium. Thus the very constitution of the branchial plates informs the anatomist and physiologist, that there cannot through them be a communi- cation from the branchial to the anal chamber. It would be lost labour to prolong this disquisition, in which I fear my observations have been too often repeated, but the importance of the problem is my apology. If I have failed to convince, I have at least supplied matter for reflection, which may perhaps lead malacologists to doubt whether the doctrine of inhalant and exhalant currents by cilia and distinct apertures can be maintained against the evidence I have pre- sented, and to admit that this long -entertained theory may prove a delusion. I conclude with a remark of Sir William Napier, who thus offers an apology all will exclaim, a needless one for writing the history of what he terms " a thrice-told tale," the Peninsular War : the eloquent historian says, " that two men observing the same object will describe it diversely, according to the point of view from which either beholds it ; in the eyes of one it shall be a fair prospect, to the other a barren waste, and neither may see aright." Are the northern naturalists and myself in this category? He adds, "wherefore truth being the legitimate object of history, it is better that she should be sought for by the many than by few, lest for want of seekers, amongst false lights, she be lost altogether." Let us then apply these views, and hope that in this branch of history many observers, besides the present controversialists, TEEEDO. 213 will step in to announce the truth and dispel the mists of prejudice. I am, Gentlemen, your most obedient servant, WILLIAM CLARK. TEREDO, Adanson. I infer that this genus is still involved in great obscurity from the serious mistakes that exist in the accounts of it : this is the more remarkable, as it has attracted great atten- tion for the last 200 years, in consequence of its devasta- tions, which have been so alarming, that various governments have called in the aid of the learned and scientific to examine into their nature, and suggest the best means of preventing them. Some authors, amongst them Sir Everard Home, call the external veins the ducts of the testicles, and say the heart is situated near the head. More modern accounts state that there is no true hinge ; that the ligament is obsolete, and the foot rudimentary or absent ; the branchise are described as long brown fleshy cords ; the elastic stylet is mentioned as a club-shaped body peculiar to Teredo, and the animal is said to be furnished with two stomachs. Some observers say, that the anterior adductor muscle is well marked, but the posterior one slightly ; others affirm the branchise to be the ovaria, and that the protective tube of Teredo megotara is destitute of the pos- terior circular laminae. I propose to show that not one of these statements is correct. I am informed that M. Deshayes has given anatomical details of one or more of the Tere- dines in his work on the ' Mollusques d'Algerie/ which I have had no opportunity of consulting ; I must therefore abide by my own views. The origin of this account was the receipt from Exmouth of a pine stake, which had doubtless served as a water-mark in one of the channels of the estuary, and being destroyed by the perforations of these creatures, was taken floating in the offing at that place. I received the mass enveloped in sea- weed, accompanied by bottles of sea-water. The log contained fifty 214 PHOLADHXE. living specimens of this rare species, unmixed with any other, many of which were apparently full-grown, and 10 inches in length ; some I examined alive and dissected fresh, and many others from spirits. These facilities have, I think, almost put it in my power to give a tolerably general idea of the animal, though it may not be a complete anatomical detail. Under the circumstances I have stated, I am inclined to think that the following notes may afford malacologists some infor- mation, and enable them to compare my humble attempt with the anatomies of Teredo by the great masters in this branch of science. Agreeably to my usual method I commence with the external description of the animal, and then proceed to its anatomy. T. MEGOTARA, Hanley. T. meffotara, Brit. Moll. i. p. 77, pi. 1. f. 6, & pi. 18. f. 1, 2. Animal vermicular, pale bluish-white, inclosed in a sub- cylindrical elongated tubular mantle, not of very thin texture, only open anteally and posteally. The specimen examined measured 8 inches from the front valves to the terminal pallets, and when the siphons were extended, an inch longer. The anterior part of the animal is inclosed in a pair of hemi- spherical sliming white valves, with a large angular gape in front, and rounded behind into auricles, which in this species are much larger than in its congeners ; the body and mantle are fixed to them, and proceed under the protection of a tes- taceous tube to the terminal pallets, which are also encased within the tube. It will here be convenient to observe, that the calcareous tube through which the body passes, to be spoken of more in detail hereafter, has hitherto been considered as one of mere protection ; but I shall show that though the globular valves in front work free in the tube, it is as much a part of the animal as the shell of the Pholades, inasmuch as it is fixed to it pos- teriorly by a very strong muscle. The brauchiffi are invisible until the mantle is opened. There is what appears to be a purple dull red labium on each side of the mouth, connected by a thin membrane ; these have TEREDO. 215 been termed salivary glands, and may perhaps be such. The oral aperture is siibtriangular. The foot in the living animal appears bluish hyaline, but when the moisture is absorbed it is muscular and coriaceous, attached to the body by a thick powerful cylindrical pedicle, and in its centre, the terminus of the hyaline stylet is visible ; the form of its basal area is that of the anterior gape, which is of a diamond figure, with its angles placed vertically and transversely, but the transverse axes are longer than the vertical. A pair of yellowish-white spatulate appendages are fixed to the posterior extremity of the body. In this animal, besides the anterior and posterior apertures of the shell, there is a rather extensive oval orifice on the dorsal surface of the shell, which is covered by a thick sub- circular tough skin, springing from the internal part of the anterior end of the mantle, which appears to have the val- vular function of closing the orifice ; but it will be mentioned again. These are the only features of the animal which are visible without dissection. A bivalve animal consists of the shell, soft parts, and the hinge, which latter organ has caused some misconceptions, which I will endeavour to remove. In this species it is nearly similar to that of Pholas ; the valves arti- culate on a thin genuine cartilage, which is a secretion from glands; on each side the anterior dorso-lateral part of the body the denticular appliances are wanting in one valve, and in the other there is only a short blunt tooth ; the ligament is a united production of the glands just mentioned, and the mantle ; it may be considered to be more external than inter- nal, and only differs from Pholas in having one, the upper, instead of two layers of transverse fibres, strengthened and covered as in that genus by the anterior end of the mantle being reflected on it, but it is not fortified by testaceous plates. We have here all but the hinge of Pholas, and taking the shell as far as its circumscribed volume extends, we find it nearly similar, in having the curved subumbonal internal apophyses, the single post-medial adductor, and the long tubular mantle fixed to the auricles ; but instead of the viscera and branchise being inclosed in the usual bivalve portion, they are placed in 216 that part of the mantle which is external to the shell ; never- theless they are protected by the tubular case, which,, as I have stated, is an integral portion of the hard parts of the animal, not merely protective or accessorial. We have thus a complete equivalent for the bivalve shells of the Pholades, in which the siphonal apparatus commences at the posterior end of the shell, deriving their retractors from offsprings of the medial adductor; whereas in Teredo the retractors have their source from a particular muscular sphincter at the posterior end of the tubular mantle in which the pallets are inserted, and have nothing of the nature of an adductor muscle, as the tube to which they are fixed is a perfect cylinder. The next point to engage attention is the muscular struc- ture, which, with slight exceptions, scarcely differs from Pholas. The two principal masses of muscles are those of the foot and the adductor ; the latter is a powerful fibrous mass of bright red filaments, as Sir Everard Home states was the colour of the species he examined ; it embraces the hinder part of the mantle within the hemispherical valves, being post-medial and fixed in the internal hollows of the auricles, showing therein when removed well-marked cicatrices : this muscle throws off elastic ribands, which proceed on the lateral parts of the mantle to that point of the tubular mantle where the sphincteroidal muscle is fixed, and of which it is probably the origin : this last muscle is a most important one ; by being permanently fixed to the animal and the posterior end of the protective tube, by the oval-shaped fillets springing from the sphincter muscle, it is the point of support for the retractors of the compara- tively short siphons, and also the fulcrum for the pallets that are firmly fixed laterally therein, and undoubtedly serve to compress and relax the siphons. It is necessary to observe, that if the very long mautellar tube was not firmly attached, the points d'appui of the pallets and retractors would be lost, and the long, linear branchise drawn together in the tube in such a mass as to impede the passage of the Avater and other functions. The posterior sphincter in Dentalium is analogous in its uses ; and though the hemispherical valves of Teredo TEREDO. 217 play loose in the anterior part of the tube, they are kept in proper position by the powerful operation and suction of the foot, and do not require permanent fixation like the smaller pallet end of the animal. I will briefly explain the operation of the posterior spatulate appendages in compressing and relaxing the siphons. The very great length of the branchiae, which are 4^ inches long, out of a total of 8 or 9, together with the extent of the tubular cylindrical mantle, requires an aid to facilitate the flow of water throiigh the long canal ; these pallets act as a sort of force-pump, and operate thus : When the branchiae require water their siphon is filled, and its inflation acted on by the spatulate valves being brought together; the sphincter is simultaneously relaxed and the water forced into the branchial cavity, after which it is again closed by the separation of the pallets, and as I have ascertained that there is no communica- tion between the branchial and anal tubes, it follows that the effete water is expelled by the same canal as it entered, by the action of the pallets on the sphincter. This is precisely the operation of the sphincter in Dentalium ; and in case a com- munication did exist between the two siphons, the anal, from its very inferior calibre, could not discharge the mass of water received by the branchial siphon into the tubular branchial compartment of the mantle ; it must either be poured forth by the anterior gape or branchial siphon--! believe from both indiscriminately. I think the anal canal is strictly applicable to discharge the water taken in by its own siphon, for rejectamental uses, and in many cases for the emission of ova. The siphons, though short, form a muscular texture of strong elastic threads, crossed by others at right angles ; the branchial orifice is usually white, sometimes pale red with eight or ten short terminal cirrhi, which are furnished with minute retractors springing obliquely near their extremities from the muscular tissue ; the anal orifice is plain. The foot is a strong muscular mass; it sends forth two very strong- fillets that are fixed to the spatulate ends of the internal crotchets, which support the body, in lieu of the ordinary 218 PHOLADIDJE. adductor muscle of bivalves, which is here, as in Pholas, wanting, to the remarks on which we particularly refer. I close these observations by stating, that the masses of the foot, medial adductor, and posterior sphincter supply their respective parts of the body with the minor muscular threads. It is time to inquire about the nervous agencies that stimulate the action of these powerful muscular organs, and we find their volume, as in Pholas, to be apparently not in accordance with them. There are just above the mouth two minute ganglia so nearly confluent that they may be con- sidered as one ; from them, two very slender threads descend to the roof of the anal aperture, distributing numerous rami- fications to the proper stomach and foot, whilst the main cords pass into the base of that portion of the tubular mantle which contains the liver, ovarium and pericardium, in a distinct independent membrane that may be called a peritoneum, and in their passage under these organs they furnish them with filaments, and then piercing the fundus of the peritoneum enter the pericardium, and form a junction with a second larger ganglion that is fixed in that cavity in some measure enveloped by the heart and auricles, and is only visible when the pericardium is cleared of them : this mass supplies the terminal part of the ovarium, the entire branchiae, and all the posterior parts of the body with nervous threads. The digestive organs next present themselves. Authors have said there are two distinct stomachs ; this is not so : they have mistaken the peritoneal cavity containing the liver, ovarium and pericardium, for one : the true and only stomach is within the hemispherical valves, in immediate contact with the greenish-brown liver that pours the bile into it from above ; it is very small ; the walls are simple ; and the elastic stylet and gizzard, which some naturalists denominate the tricuspid membrane, work within it as a gizzard and attritor. I have carefully dissected the apparatus of the present species, and have it on a card in a united state, showing the hard horny parts of the rubbing portion. Some authors say that this machine is not to be found in all bivalves. Which are without it ? I am inclined to think that it is absent in none. TEREDO. 219 The mouth is a triangular V-shaped aperture placed imme- diately above the foot; on each side there is a palpar or salivary mass, which from its wavy streamlets appears to be of the latter quality; they have a glandular aspect, and may perhaps combine tentacular uses. The mouth opens into a short O3sophagus which descends into a small stomach, the contents of which under the microscope appeared to be wood reduced to a pulpy mass, that, after having undergone the action of the gizzard, is discharged into the intestine, which, as soon as it springs from the pylorus, mounts to the integu- ments that divide the dorsal aperture from the peritoneal cavity, passing through them and showing from without a tubular inflation that has been mistaken for the oesophagus of the second stomach, but is undoubtedly an intestine, which I have traced and opened throughout its length. It proceeds in a straight line through the liver to about the centre of the ovarium for 1 inch -iVths, when, by a sudden short turn, it retraces its steps for f^ths of an inch, when it again turns and makes an oblique reach of about | an inch ; it then makes a further gyration, forming a complete but small sigmoid flexure, and pursues its course for 1 inch -j^ths to the anterior part of the body, which it descends, coasting for Wths of an inch the foot to the external pyloric point of the stomach, and, becoming a short rectum, opens into the tubular mantellar canal at some distance from the anal siphon; the whole of the cir- cumvolution is about 5 inches, far exceeding that of the Pho- lades. The valvular dorsal flap before mentioned covers the aperture under it, assisted by a fine membrane perforated to correspond with the oval aperture, which appears to be in aid of the external valve for preventing the ingress or egress of water, except at the minute perforation in unison with the true mouth. I can conceive no other use for this valve than to admit water to the mouth, oesophagus and stomach when the foot is engaged in excavation, and in consequence perhaps the anterior gape is hermetically closed. It would appear that the animal swallows the excavated wood, and does not eject it by currents of water. I infer this, as not only the stomach but the intestine is always filled with 220 PHOLADIDJS. a pulp, which under the microscope has the aspect of ligneous debris. The Patellae operate in like manner. The circulation is venous, arterial and branchial, and con- sequently complete. The respiratory apparatus has been strangely misunderstood ; it has been described to consist of four fleshy cords, portions of which Sir Everard Home pro- nounced to be the testes, and others the ovaria ; these views are erroneous. But we will first mention the heart and auri- cles, which are placed at the base of the ovarium in the peri- toneal cavity within the mantle, but in a distinct pericardium ; the heart is an elongated, very pale bluish-white opake ven- tricle, accompanied by two symmetrical fusiform slender auri- cles that are also opake, somewhat posterior to it, which appear to pour the aerated blood into it by lateral valvular ducts. On opening the ventricle its walls did not exhibit any particular muscularity : we were not successful in detecting the valves of the auricles. There is at the posterior part of the auricles a white, suboval, subglobular, fine granular mass, touching and partly surrounding them; we are unable to state its nature ; it is not part of the ovarium, which termi- nates before the pericardium commences, and in such a situa- tion it cannot be the organ to aiiimalize the ova : we are in- clined to consider it a gland that distils a liquor for the use of the heart and auricles. At the base of these organs the four cords that have created such difference of opinion as to their uses come into view, but they do not appear to be either the branchiae, arteries, veins, testes or ovaria ; still they have a sort of connection with the branchiae ; the two longer and larger brown lines have their origin on each side the hemispherical valves, and proceed, attached to each latero-dorsal range of the mantle, to the posterior siphons ; they appear to be composed of red-brown granular points ; within these two lines, but not until the branchiae commence, two others of smaller size and nearlv / similar composition run parallel, and terminate with the larger ones at the siphons; the addition of the two shorter and smaller cords springing from the larger at the point where the branchiae begin, appears to show a connection of these TEEEDO. 221 appendages with them, whatever their nature may be. We will now consider the structure of the branchiae, and the surmises on the nature of the four brown cords that accom- pany them. The branchial apparatus is composed of only two narrow laminae running horizontally from their origin, where they are the broadest, attached to the dorsal region of the mantle and tapering gradually to the siphons ; but before they approach them, for an inch or two, they become more fleshy and linear, and are what Sir Everard Home terms " the strong substance for the support of the Aveakest part of the body of the ani- mal ;" they do not enter the siphon, as in Pholas, being cut off therefrom by the posterior sphincter ; their colour is red- dish-brown, and the blood, as seen by the microscope, very pale pink ; their length in a nine-inch animal is from 4 to 4^ inches. The branchiae in the living animal are doubled together and hang on each other, but without the inter- vention of any substance between them, and in this respect are similar to the branchiae of the Pholades when they have cleared the body and become linear : but in Teredo they are altogether posterior to the body. The branchial artery of each lamina runs, as usual, parallel, and just under their junction with the body, in the closest connection with the granular cords in question ; but each branchial vein runs parallel and decidedly within the granular cords, and shows no connection with them like the arteries. What then is the nature of these appendages, particularly of the longer ones ? I am inclined to consider them glandular bodies, which perhaps serve either as emuiictories, to carry off injurious matters from the blood, or as absorbents of what is beneficial : I am quite at a loss to say which of these very opposite views is most probable. I will state another surmise: they may be an aid to extract additional quantities of air to invigorate the branchiae in the production of the utmost vitality for the blood, to support the animal in the arduous labours of excavation : in this view they may be considered as rudimentary branchiae ; but after all is said, their true functions are doubtful. With respect to the secretions, all that I know of them 222 PHOLADID^E. has been mentioned under the heads of the organs I have described, except those of the ovary, which will be noticed hereafter. These animals, like all the Bivalves, are strict hermaphrodites. The ovarium is a white glandular body entwined with the liver, but as it approaches the pericardium it becomes a distinct mass ; and, what is unusual at this time of the year (20th January), in several of the ovaria the contents had begun to assume the appearance of ova; but with the utmost power of the microscope I could not perceive any trace of the membranous pyriform bodies containing a fluid which I have observed in the genial months in many of the ovaries of the strict hermaphrodite Bivalves and Gastero- poda, which I consider to be the male influences ; nor could I discover any other organ that had the slightest pretension to be regarded of a similar nature. I failed to verify the oviduct, but from the position of the ovarium I have little doubt that it passes at and under that portion of the peri- toneal cavity which contains the terminus of the ovary, into the anal compartment of the mantellar tube, about 1^ inch above the siphon, and that the ova are there discharged. I do not think the branchiae in this species serve as re- ceptacles for the ova ; their structure is not calculated for such purpose. I will now make a few observations on the camerated structure of the posterior part of the protective tube, which has caused malacologists much speculation on its uses ; some, myself amongst others, thought the laminar spaces might be to protect the pulli for a time until ultimate exclusion. These ideas were dispelled by the discovery of the fixture of the posterior part of the animal by the strong oval muscles springing from the sphincter, which induced me to examine this portion of the tube with care, and in a fine full-grown specimen I discovered the principal object, if not the precise animal ceconomy, of the laminae. I perceived in the centre of each plate a decided muscular impression, which, on compa- rison with the last-formed one of the sphincter muscle, proved to be identical in shape ; this fact made it evident, that the animal, either when full-grown, or when growing, if its longi- TEREDO. 223 tudinal increase is not correspondent with the boring progress, must, by being posteriorly fixed, either suspend excavation, rupture the mantle, or have the power of advancing the muscle of attachment. This advancement of the muscle is not a new fact ; it has been observed in the Spondyli and Ostrece ; and it cannot be doubted that nature has conferred on the present species the power of detaching and advancing the muscle of attachment, and that each hoop-shaped lamina, thrown out for some point of the animal O3conomy, marks the periodic removal of the muscle. The laminse are always more nume- rous in the longer and older animals ; in very young specimens there are only 1-3, and in the older ones 20 iO. When authors have stated that this species has the tube without concamerations, we presume they have only had opportunities of examining very young or imperfect speci- mens ; in all the specimens I have seen, many of which were 10 inches long, they were present, and I belive that no species of Teredo is without them. The plugging up of the terminal volutions inAporrha'is and other Gasteropoda, and the consequent withdrawal of the posterior parts of the animal, are analogous to this operation in Teredo ; the same principle excites the action in both cases, self-preservation. It will be observed that the alliance of Teredo with Pholas, through the apophysary processes, is more decisive than be- tween any two other bivalve families. I trust that I shall not be considered fanciful if I venture to remark, that there are points of analogy between Teredo and Dentalium so striking as almost to give some weight to the idea that it forms the passage to the Gasteropoda ; in support of these views I beg malacologists to observe the similar vermiform character of the animals, the attachment of their posterior parts to the shells by sphincteroid muscles, the peculiar plan of the admis- sion of the water by short siphons in conjunction with the sphincter, the single branchial dorsal lamina on each side, their separation from the body, and other minor analogies. These concordances almost make me think my hypothetical surmises have some foundation, and that the transfer of Pholas 224 and Teredo, &c., from the bottom to the top of the scale of the Bivalves, is not an injudicious procedure. The other British Teredines are T. NORVEGICA, Spengler. T. norvegica, Brit. Moll. i. p. 66, pi. 1. f. 1-5. T. NAVALIS, Linnseus. T. navalis, Brit. Moll. i. p. 74, pi. 1. f. 7, 8, and pi. 18. f. 3, 4. The following are exotic : T. B i PEN NAT A, Turton. T. bipennata, Brit. Moll. i. p. 80, pi. 1. f. 9-11. T. MALLEOLUS, TurtOll. T. malleolus, Brit. Moll. i. p. 84, pi. 1. f. 12-14. T. PALMULATA, Lamarck. T. palmulata, Brit. Moll. i. p. 86, pi. 2. f. 9, 10, 11. XYLOPHAGA, Turton. X. DORSALIS, Turton et Auctorum. X. dorsalis, Brit. Moll. i. p. 90, pi. 2. f. 3, 4 ; and ii. p. 375. We met with this species alive many years since, at Ex- mouth, and greatly regret that it passed unobserved. Having inserted a paper in the 'Annals of Natural History' on the Terebrating Mollusca, we will only state, that it is now generally considered that the foot and fleshy part of the ventral surface of the mantle, aided by the fine sand and siliceous particles that are a part of the animal's attributes, are the excavating agents. See Mr. A. Hancock's excellent Memoir on these points, in the 'Annals of Nat. Hist.,' N. S. ii. p. 225. DENTALIADJ5. J>25 GASTEROPODA. That this division of the Mollusca is the sequence of the Bivalves is universally acknowledged ; this is shown by a body of facts that are familiar to all who cultivate this branch of science ; but it is also evident that the Gasteropoda have very decided marks of an advancement to superior organization ; the distinct head, eyes, tentacula, denticular apparatus, the cesophagean concentration of the medullary ganglions, the character of the foot, the almost invariable state of freedom and consequent increased facility of locomotion, together with a greater complexity of the generative developments of many of the families, are sufficient proofs of a great progress in animalization. It is not necessary here to enter on anatomical remarks, as almost every point connected both with the internal and ex- ternal animal structure is again and again mentioned in the observations concerning the different families ; it would there- fore be a useless repetition to extend our notes in this direction, and we at once proceed to introduce the respective families, only premising that there are still some gaps in the descriptions of the animals, but these deficiencies are daily disappearing in consequence of many recent discoveries. DENTALIAD.E. We are obliged to provide for this family of one genus, a distinct branchial section, which, from the symmetrical lateral disposition of the branchiae, we have termed Lateri- branchiata ; we consider this arrangement subject to our determination of the branchiae being confirmed. Large ana- tomical details of the Dentalium Tarentinum are annexed. From my observations in the ' Annals of Natural History/ Q 226 DENTALIAD.E. 1849, it appears that the minute species of the genus Ccecum, from their configuration, have generally been located with the Dentalia, though it will be seen that there is little concordance between the animals of the two genera. I believe, with the exception of M. Deshayes' monograph, that nothing has been done to elucidate this curious molluscuin ; and as I think that eminent malacologist has mistaken the uses of some of its organs, I am induced, by the facility of obtaining live speci- mens of the Dentalium Tarentinum, to review and augment what is at present known of it. The animal exhibits a series of characters of the highest interest, in its anatomy and functional developments, some of which are so anomalous, that it must be considered one of the most singular of the testa- ceous mollusca. DENTALIUM, Linnajus. D. TARENTJNUM, Lamarck. D. Tarentinum, Brit. Moll. ii. p. 451, pi. 57. f. 12. Animal yellowish- white, conically elongated, mantle circu- lar, anteriorly thick and fleshy, edge dentated, posteriorly of the thinnest texture; the penultimate and antepenultimate portions of its margin are bounded by two intense white mus- cular elastic cordons; the united action of these has the power of completely opening and closing the anterior aper- ture ; when at rest, the animal, including the foot, is entirely enclosed by the tougher part of the mantle which supplies the place of an operculum. The foot is a very long and singular organ, placed in the centre of the anterior end of the body, and from its position is applicable for use in every direction ; it is divided into three parts : the anterior one is a pointed cone acting in some measure as a tentaculum, and lies in the middle portion, which consists of two lateral, sinuated, symmetrical flaps or tena- cula, that are usually protruded simultaneously with the terminal portion, and are the parts subservient to the animal's very confined locomotion, by using the lateral appendages as DENTALIUM. 227 points d'appui to turn from side to side, and also to climb and secure its food from the stems of the foraminiferous polyparia ; the third or basal section is a long flattish pedicle, deeply grooved on its upper and lower surfaces, extending to the base of the stomach, into which it opens, as it is hollowed out as far as the tenacular flaps, but there is no passage to the exterior surface. I have failed to discover the reason for this connection with the stomach : the hollow part is filled with water, but from what source does not appear, though I think it must come from the buccal aperture. The use of this singular structure is clearly to augment the flexibility of the foot, as the animal frequently and suddenly doubles it up as the elephant does its trunk ; and also to withdraw the two anterior parts into the hollow portion : this retractile action is necessary in consequence of the pecidiar mouth of the ani- mal and the rigid character of the anterior end of the mantle, to convey the sustentation captured by the tenacula into the . cavity of the mantle within the reach of the very short folia- ceous cirrhi at the buccal orifice. From the foot an elastic fibrous riband runs, on each side of the body, to the posterior terminus, and affords the animal the power of greatly con- tracting and dilating that end of it, as may be seen by the creases of contraction, which in some degree give the ap- pearance of annulations. At the base, and above the pedicle of the foot, if that sur- face of the animal is upwards which lies in the concavity * of the shell, and vice versa, in the convexity, is inserted a distinct light yellow tubular buccal appendage, without eyes or tenta- cula, which can only be considered a kind of external osso- phagus, and as regards its accessories and form, has no pre- tensions to be styled a head ; it is encircled by about eight or ten short dendroid tentacular strands ; its cavity forms two extremely dilatable pouches divided by a longitudinal septum, which become compressed and merge apparently into one at the point of passage into the stomach. These external re- ceptacles invariably contain from ten to forty, or even more, * Concavity is dorsal, convexity is ventral. M. Deshayes states the contrary, but he is mistaken. Q2 228 very minute Foraminifera, a convincing proof of the voracity of these animals. I have never failed to find in them either the Quingue-, Tri-, or Bi-loculince, or the Rotalia Beccarii, the Lobatula vulgaris, Bulimina pulchella, Textularia oblonga, Lagena amphora, or the Robulina subcultrata, and more rarely a minute bivalve, either the Kellia suborbicularis or Astarte triangularis : this fact is another proof, if any additional ones were necessary, that an animal inhabits the minute calcareous forms which were formerly supposed to enclose Cephalopoda, or to be inserted in their membranes : they are not inhabit- V ants of the littoral, but of the coralline zones, and appear to be the sole aliment of this decided zoophagous mollusc. These shells are in transitu to be acted on by the appendage within the stomach, which will be noticed shortly, and after having undergone its action the rejectamenta are discharged anteriorly with other mucal and faecal matters, and not at the posterior terminus agreeably to M. Deshayes' determination; and I shall presently demonstrate that the posterior aperture is not for anal uses, but to supply the branchiae with water. It is now necessary to mention the figure and situation of the heart and branchiae ; these points must be carefully kept in mind, as the demonstration I propose rests on a due consi- deration of them. The heart is a subrotund minute ventricle with a linear depression on its summit, and when opened shows the corresponding ridge ; its surface is fortified with muscular raised lines ; it is fixed centrally at the posterior end of the branchial cavity and base of the stomach, and in some transparent animals may be seen in the pericardium ; in the very young pellucid shells seven inspirations and as many nearly isochronal expirations have been counted in a minute, and the corresponding ingress and egress of the water seen *. * Lamarck, in the last edit, of the 'Anim. sans Vert.' (Milne-Edwards's) 3rd vol. p. 13, says, " Car, apres les animaux vertebres, la nature n'offre, dans aucun animal, ces mouvements alternatifs et mesures d'iuspiration et d'expiration du fluide inspire," &c. On this point that great naturalist is in error, as in Dentalium Tarenti- num I have, with a chronometer showing seconds, repeatedly marked nearly isochronal inspirations and expirations of the aerating fluid, the two toge- ther amounting to about sixteen in a minute. DENTALIUM. 229 I have not detected auricles on each side of the heart, nor near it, as might be expected from the symmetry of the branchiae ; there are certainly minute points on each side of that organ, but I object to call them auricles, and rather think they denote the valvular appendages of the heart, to pre- vent regurgitation into the branchial veins. The blood of the posterior part of the body is brcmght to the branchial artery which runs at the inner base of the branchiae, by two longi- tudinal veins, which pass between the branchiae on their convex surface, receiving tributaries ; I could not trace those of the anterior part. The arterial blood is then distributed into the ramifications of the branchiae, and after aeration is passed by each principal vein, which coasts the edges of those organs at their dichotomous points, to the heart, which throws out a posterior and anterior short trunk, both of which bifurcate into two smaller arteries, which supply veins infusing a re- newed vitality into all parts of the body, from whence the blood is again returned to the arterial centre. Under the microscope the blood of the tributary and superficial veins appears to be in some individuals of a pale pink colour, and in others of a purplish pale red cast. The branchiae are two symmetrical, sublateral, and some- what post-centrally situated, dark greenish-brown, elongated, suboval organs, having their bases fixed on and hanging from the concave surface of the animal, with their points vertically parallel to the bases ; the two branchiae are united at their inner surfaces by a bridle of branchial strands arranged sym- metrically. The heart in the testaceous Gasteropoda, spiral and other- wise, is always placed at the posterior end of the branchial cavity, or, in other words, is fixed at that extremity of the branchiae furthest from the entry of the aerating fluid *. This * M. Milne-Edwards has placed a few genera, as Bulla, Pleurobranchus, and Aplysia, in his division Opisthobranchiata, as having the heart anterior to the branchiae. Without closely considering the merits of his arrange- ment, which perhaps is fine-drawn and not constant, we may say, in respect of the case between M. Deshayes and myself, that it does not bear upon it, as, in whatever way the question is looked at, Dentalium is a strict proso- branchiate animal, with the branchiae anterior to the heart. 230 DENTALIADJE. statement of position is of importance in coming to a con- clusion as to the mode of entry of the water. But if the position of the organs of Dentalium be examined under the view of the water approaching the branchise under the mantle, as in the ordinary Gasteropoda, they will be found to be the reverse of what I have stated to be the usual natural position ; the heart will be found at the anterior end of the branchial cavity instead of at the posterior, and nearest to the entrance of the water instead of furthest from it : here is a subversion of the order of nature in respect to the position of these essen- tial organs : how are they to be placed in harmony with her laws ? The solution of this question is simple : we have only to consider that the water in this genus flows to the branchise by the posterior aperture instead of at the front ; this view removes every difficulty, and may be regarded as a demon- stration of the fact, which is satisfactory and decisive, because it is founded on the organization which nature has conferred on these animals. I will state some facts in support of the conclusion that the branchise in Dentalium receive the water posteriorly. I admit that, notwithstanding a constriction, it may possibly enter in front under the mantle and be discharged posteriorly, and vice versa but this action would be contrary to the natural posi- tion of the organs and to the evidence I shall now adduce. But first it will be necessary to mention the mode of fixture of the animal to the shell : this is not at the centre, as in the spiral Gasteropoda, but at the posterior end, a little more than an eighth of an inch from the terminus, where, on the inner surface, may be seen the strise, in the hollows of which the fine filaments, issuing through the mantle and proceeding from the longitudinal elastic riband running from the foot, are depo- sited ; and, together with the strong sphincter of the posterior process, which is imbedded in an indentation not visible from without, firmly secure, by constriction, that end of the animal to the shell. This is a striking example of the admirable adaptations of nature of the organs of animals to their wants and (economy ; for if this animal was fixed to the middle of the shell as in the spiral ones, the contractibility of the poste- DENTALIUM, 231 rior part of the body would be destroyed, and its vermicular motion, to aid and accelerate the passage of the branchial fluid and its expulsion through the comparatively narrow medial duct, paralysed. I may state in corroboration of the foregoing observations, that I have removed the posterior hyaline process and enlarged the orifice as much as possible, and then dropped therein some grains of fine sand to irritate the membranous spoon-shaped process, when instantly pure water, without the slightest admixture of fsecal substances, was ejected ; and this result was invariable in all, and many, individuals. I have stated that in young transparent specimens an unin- terrupted but slow action of systole and diastole might be observed, and was apparent from the distinct ascent and de- scent of the water in the branchial canal ; but this action cannot take place in a merely excretory tube ; it can only exist in a circulatory, or inhalant and exhalant one. I have carefully dissected the body from the branchise to its terminus, and submitted its substance to microscopic powers, without discovering a trace of an intestine, which is usually the easiest organ to be detected by its colour and distension. I have carefully watched thirty individuals at a time, and never saw any rejectamenta from the posterior process ; but in the same period frequent discharges anteriorly from the centre of the mantle, of foraminiferous spoil enveloped in mucus. I finally observe, that on the animal being removed from the shell, the medial branchial canal is distended, but in a short time collapses from the evaporation of the fluid, and exhibits a deep canaliferous groove; and when the canal is not quite full, one or two globules, precisely like those of a spirit-level, may be made with the slightest pressure to float backwards and forwards from the posterior sphincteroid process to the branchiae. Many other circumstances can be added in proof of the posterior entry of the branchial water, but I have already transgressed the limits of conciseness, and it is time to take some notice of the nervous system, salivary glands, the stomach and its contents, and the substances which fill up the body from the branchise to the posterior terminus. 232 DENTALIAD.E. At the base of the oesophagus is a cerebral mass of four minute, pale pink, subcircular, finely-punctured ganglions, in form somewhat like the letter X, united by a nervous thread or collar, which encircles the oesophagus at the point where it passes at the base of the foot into the stomach, and the fine filaments therefrom are distinctly visible passing to the stomach and throwing off anastomosing lateral threads ante- riorly to the foot, buccal orifice, and the other front parts of the body. The salivary glands are very large, covering the base of the foot and the ossophageal ganglions, and envelope the buccal pouches so completely that they seem imbedded in them ; they spring from each side the base of the mouth, and are two thick fasciculi, which consist of a multitude of very fine, long, light yellow capillary strands ; their extraordinary volume is necessary to produce a copious supply of fluid to lubricate the enormous quantity of Foraminifera these animals swallow, especially of the scabrous ones, as Bulimina pulchella, and the sharp-pointed Lagena amphora. The oesophagus, after emerging from the nervous collar, instantly enters the stomachal cavity, which is composed of a muscular membrane of a broad oval form, the anterior and larger portion thereof being occupied by an extremely strong gizzard, formed of a pair of subelliptical folding jaws with eighteen laminae bent towards the points on each side, and studded with very strong blunt teeth : this denticular frame is supported by fleshy lobes encased in corneous plates, and appears to be an organ nearly similar to the buccal mass of the ordinary Gasteropoda ; it is not however placed, as in them, immediately at the anterior orifice of a pharyngeal oesophagus leading to a stomach and fixed thereto by strong elastic threads, but it is the stomach itself most slightly attached to the membrane which envelopes it. This powerful machine undoubtedly acts as a gizzard, to grind the testaceous food of this animal ; it empties itself by a very short scoop- shaped canal into an intestine of three or four intricate Gordian knot-like folds, which, strange to say, often contain a dozen or more shells that have escaped the action of the DENTALIUM. 233 gizzard. The intestine does not entwine with the liver, but is enclosed within the same cavity as the gizzard ; it pierces its enclosure on the right side, passes through the liver, and discharges the rejectamenta at the base of the branchial cavity, under the mantle about the middle of the shell, from whence they are passed, by the deep groove of the foot, which the animal can, by the compression of its sides, make canaliferous, as far as the middle section of the foot, around which, when the animals are fresh from the sea, they form repeated collars of mucus, which in a short time, from frequent aggregations of matter, become ponderous, break and fall off, and when examined are found to be composed of the spoil of shells : this circumstance, independent of all others, shows that the fseces are not discharged posteriorly. The liver is an extremely scanty light yellowish-green organ placed under the stomach, and is continued under the branchial cavity, and then joins the ovarium, with which it becomes almost imperceptibly amalgamated throughout its whole length. The ovarium is very long and large, and fills up the whole of the posterior part of the body from the branchiae ; it consists of from four to six longitudinal rows of distinct granular yellowish-white masses of ova, with scanty interweavings of the liver, which exhibit three stages of de- velopment ; the more forward ones become broken into six portions, and when ready for exclusion these again break into perfectly round, pale brown globules ; all these phases vary in different animals according to the advancement of fecunda- tion. The oviduct is in the centre of the longitudinal rows of ova, formed by their junction, and the ova are undoubtedly discharged by the posterior spoon-shaped process, from whence I have seen volleys of fifty or a hundred ejected with con- siderable force in minute round points : these must not be mistaken for faecal pellets, neither must the oviduct be con- founded with the branchial canal, which is the cavity formed between the mantle and the membrane of the ovarium. The homogeneity of the masses of this part of the body in many conditions, especially when fecundation is not far advanced, 234 DENTALIAD^E. renders the discrimination of organs of this character a matter of some difficulty. I have not discovered any exserted organs of reproduction, and I think from various considerations that this animal is an hermaphrodite, but without congression. Under the microscope, in the midst of the general mass, several small egg-shaped globules, having at one of the axes a minute, apparently tubular filament filled with a glairy fluid, may be seen in some individuals, but not in all, as I have sometimes searched in vain for them ; these may be the virile fecundating organs, which are perhaps only apparent at certain stages of gestation. I have extended these observations to an unusual and almost inconvenient length : the carious and anomalous structure of this mollusc, and the multitude of interesting characters attached to it, exhibit such modifications of the organs of the typical Gasteropoda as appear to give it a claim to be considered as the point of transition from the Bivalve Mollusca to the great change in figure and faculties which nature has produced in the superior developments of the Gasteropoda ; and perhaps, from a review of this account of these organs, rnalacologists may be induced to think that it will appropriately form one of the first, if not the first link, in the chain of the Gasteropoda. The symmetrical subventral position of the branchiae, the posterior flow of water to them, and the resemblance of the foot to that of some of the Bivalves, combined with the similar character of its action, appear in a striking manner to show its connection with the Conchifera ; whilst by its ossophageal cerebral ganglions and completeness of the circulation, it has established its claims as a Gasteropod. There are also traces of alliance with some of the inferior classes : the red blood and vermiform configura- tion of the posterior part of the animal show some of the characters of the Annelides; but though we acknowledge these sources of its origin, we cannot fail to see how clearly the animal of Dentalium displays at varioiis points the progress of advancement, and the ameliorations nature has so bene- ficentlv effected in its animalitv. DENTALIUM. 235 The present species inhabits the coralline zones of the South Devon coasts, five or six miles from land, in twelve or fifteen fathoms water. I had written thus far when I received from Paris M. Deshayes' memoir on the Dentalia, which I had not seen for twenty years, and its contents had nearly passed from my memory; on looking it over I find that the differences be- tween that gentleman and myself are more important than I was aware of, but I am not inclined to abandon my own views. I am also "glad to find that I am enabled to fill up many gaps as regards the functions and habitudes of these animals. This gentleman, in stating the anus in Dentalium to be posterior, observes that it is the only molluscum that has it so situated; but this anomaly, if it be so, I think I have disposed of. Those organs which I consider to be the symmetrical branchiae are termed by M. Deshayes the lobes of the liver, each pouring into the stomach the bile by their biliary vessels. I cannot persuade myself that this view is correct; I have submitted them to the microscope, and in each principal strand I have seen the leading vein distended with red blood, as well as the net-like connecting ramifications; I there- fore consider what are called the biliary vessels to be the branchial veins conveying the blood to the heart instead of bile into the base of the stomach. M. Deshayes in his figure has omitted to mark the vein which runs at the dichotomous points of his organ, which, when viewed under high powers, is very visible, and which I take to be the branchial vein. What I term the salivary glands, are the branchiae with M. Deshayes, combining the functions of tentacula : he does not mention such glands. I must consider this assumption in- correct ; and to support this opinion I state that the heart is separated the whole length of the stomach from the bases of what M. Deshayes terms the branchiae : this is a position without parallel, as that organ is invariably in the closest 236 contact with one end of the branchiae. That naturalist cer- tainly connects the two organs by stating, as I think erro- neously, that the heart sends great and numerous vessels to the branchiae. Now, the heart never transmits blood directly to the branchiae, but impels it into the system by arteries and veins, from whence, as I have already stated, it reverts to those organs. The filaments in dispute I have submitted to microscopical observation; they only present the appearance of a compli- cated mass without a trace of particular arterial and branchial vessels, and they have nothing like the symmetry of branchiae ; I believe them to be merely secreting glands, and they may perhaps combine tentacular functions. M. Deshayes is, I think, in error in stating that the aliment undergoes a second mastication : this idea has arisen from his having divided the gizzard into two parts, one of which he describes as " machoires," and the other as an " appareil dentaire assez complique :" the fact is, there are no hard parts in the buccal pouch ; which, when removed, there being no internal oesophagus, exposes to view the anterior part of the gizzard, which is likened to two spherical black points gaping like a small bivalve : these are only part and parcel of a whole the gizzard, which may almost be called the stomach itself, as it fills the entire stomachal membrane, with the exception of the convoluted intestine at its base ; consequently the aliment has no other mastication but of one denticular apparatus. That there are no errors in these observations woidd be an undue assumption; for who, on such subjects and in the examination of these minute objects, can hope to escape from occasional error? I invite malacologists to offer their cor- rections, if I have differed on insufficient grounds from so eminent a naturalist as M. Deshayes ; and I conclude with the evocation, Si quid novisti rectius istis, Candidas imperti. DENTALIUM. 237 D. ENTALIS, Linn, et Auct. -D. entails, Brit. Moll. ii. p. 449, pi. 57. f. 11. I have only seen one live specimen of the D. entails ; the organs have the same characters as those of the Tarentinum, but it is very distinct; the colour is snow-white, and on comparison of two shells of the same size, the D. entails will be found much more slender ; the branchiae are of a paler green, more scanty, thin and delicate. Having had good opportunities of reviewing my notes, I have thought that it would be desirable to mention the result ; and I am the more anxious to do so, as I have the misfortune to differ on all essentials with zoologists whose talents have long stamped their judgment on these subjects as authorities scarcely to be disputed. I am unable to make any material correction in the preceding observations ; I can only add some fresh incidents and offer a few explanations. In carrying out these views I must again allude to M. Deshayes' and his coadjutor M. d'Orbigny's monograph ; it appears to me that there are in it some misconceptions, in addition to those I have already pointed out, which if passed over may mislead. M. Deshayes says that the convexity of the shell answers to the dorsal range, and the concavity to the ventral ; the reverse is the case, as I have proved in a hundred specimens, unless it be contended that the foot is placed above the head or buccal pouch on the dorsal range, instead of being under it on the ventral line, agreeably to the order of nature. Again, the heart is stated to be fixed on the dorsal surface above the stomach, and in the figure delineated it is lying on that organ and exceeding it in length ; but repeated examinations inform me that what is called and figured as the heart is the masti- catory apparatus and intestine, which He in the stomachal cavity, and demonstrate their presence by a marked inflation. The heart, as I have mentioned, is a minute organ at the base, but separated from the stomach by a septum or rib, and immersed in the centre of the dorsal and ventral surfaces ; 238 DENTALIAD^E. it cannot be well seen from the dorsal area, but in transparent individuals may often be observed in the pericardium from the ventral surface, without dissection, between the bases of the stomach and branchiae. The following remarks give a more correct view of the character of the liver. The real liver not my branchiae, which M. Deshayes states to be the liver consists of two symmetrical subcentral masses, one on each side, formed of 10-15 subrotund, pale to dark brown granular lobes, and of each group the biliary duct can be observed to pierce the peritoneum. With regard to the salivary glands - M. Deshayes' branchiae I have again examined them, and traced their pedicles and ducts to spring on each side of the O3sophagus at its junction with the stomach, and, as I think, supply the buccal pouch with a lubricating secretion to assist deglutition. I can discover no connection between the heart and these organs. All examples show that the foraminiferous faecal spoil is discharged anteriorly, and I think that there can be no question of the entry of the bran- chial water by the posterior canal, which, with M. Deshayes, is the anal conduit. As a positive proof of this arrangement, I repeat, in confirmation of my former statement, that in many young delicate pellucid individuals, I have both by sun and artificial light seen the water, in whatever position the shell is held, ascend and descend in the tube for /the aeration of the blood, by alternate contraction and dilatation ; in fresh animals the inspirations and expirations are, each, 5-8 in a minute, or together 10-16; but when they have been kept some days and suffered from want of food, the times of the two actions are more irregular and fewer ; and still more so when the water has become effete, by the animal being long detained under examination : these processes can be observed for many days until nature is exhausted. I submit that these are strong reasons in support of the posterior admission of the branchial water, and that what has been called the anal issue is undoubtedly the aquiferous canal. I again beg to impress on zoologists, that no organ of simple depuration or excretion is ever under systole and diastole influences. CHITONID^E. CHITONIDJE. Before I enter on this family, I beg to state, that a more extended experience of the Mollusca has compelled me to relieve myself, in part, of the assistance of conchological attri- butes, as I have found them singularly defective and fallacious in reference to the existing constitutions of divisions, families and genera. I therefore, as regards the past, and henceforth, shall only consider the shell-coverings of the Mollusca as good and useful aids, in strict subservience to the malacology of the animal, and as consequential specialties emanating from the vital organs ; and that the meaning of whatever appellation may be attached to a division, family or genus, has with me no reference to the testaceology : for instance, speaking of the Muricidce, or its synonym, the Canalifera, the shell is not in question, except as a corroborating incident, but the animalia canalifera, whose mantles form canals; and in like manner, in mentioning the Holostomata, the entire periphery of the aperture is not primarily intended, but, that the mantle lining it is entire. The use of the word ' shell/ instead of ' animal/ in the con- struction of the subordinate divisions of a class, has doubtless arisen from the ignorance of naturalists of the inhabitants ; but as this cause is in a great measure removed, it is time to abandon a system founded on fallacious bases, and have recourse to nature's imperishable land-marks. In these observations, I do not mean to say that conchology is without its use : to palaeontologists, collections of shells are the only resources to denote that their fossils present similari- ties to many existing forms ; but how infinitely more valuable is an account of an existing animal, to inform them of the real character of the relics of former epochs ! Beyond the re- stricted points, conchology is totally unworthy to be the suc- cedaneum of the attributes of nature, and the true worshipers of the great book will rejoice at the decadence of a usurpation to its just limits. 240 The Chitons have long been a source of difference of opi- nion with naturalists, not only as to their position amongst the Mollusca, but it has been insisted on, that they are apo- cryphal members of that class. The greatest authorities are in collision : M. De Blainville considers that the motive power and other apparatus of the circulation have a rectilinear .dorsal arrangement, similar to that of the Annelida : Cuvier and Lamarck regard them as true Mollusca, ranging with the Patelloid group : Professor Forbes has doubts, and looks on the question as still within the limits of debateable ground, and terms the Chitons malacological " puzzles." Some ob- servers contend, that the reproductive organs, unlike the asymmetrical ones of the Gasteropoda, exhibit a disposition of parities on a medial line, and like M. De Blainville refer them to the Annelida. Milne-Edwards demurs that they are Mollusca, and goes no further than to regard them as an aberrant tribe of Gasteropoda. Having dissected many examples of three species, I think that my notes may assist zoologists in coming to soimd con- clusions with respect to natural position. As my investiga- tions have induced a chain of reasoning which has convinced me that the Chitons are true Mollusca of the Patelloid type, it may be as well at once to allude to that part of them which bears upon the objections that have just been stated. Though doubts have lately sprung up as to the natural position of these curious animals, they have, until now, been placed by most authors in close connection with the Conchi- fera. If this is right, what then is there extraordinary and unusual in the disposition of the organs of the circulation ? They have nearly the same dorsal rectilinear position as in the Acephala, from which they have long been considered, and I think it will be shown rightly, the point of transition to the Gasteropoda. Why not, therefore, contrast this peculiar arrangement, which is the invariable consequence of the sym- metry of the bivalve animal, with that which obtains in the Chitons from the same cause, and also in others of the Patel- loid tribe that have the same position and a similar parity of their organs? I admit, that the strict Patellae, though CHITONIDJE. 241 symmetrical in their testaceous cones, are exceptions with regard to the heart, auricle, and branchial plume : Haliotis, which with me is a patelloid animal, and also an exception, is the reverse, having the organs of the respiratory circulation symmetrical, but not the cone. These, and two or three other genera, may be regarded as the precursors of the Gaste- ropoda, and as points of transition from the strict parities of the cone of the shell and organs of the Patelloida, to the asymmeti-ical division of the Gasteropoda. The only differences, and they are not important, with respect to the position of the circulation in the Bivalves and Chitons are, that in the latter the motive power is placed greatly more posteriorly than in the former ; and the illus- trious Cuvier has taught us to observe, that the auricles of the Chitons have a quadruple connection with the heart, of which he has seen no other example in the animal kingdom : this is not stated in an objective sense, but as a curious fact, though he gives no reason for this aberration of the usual structure. Enough has now been said to demonstrate the little value of the much-insisted-on dorsal rectilinear position of the motive power of the circulation in Chiton, in comparison with the Annelida. As to the objection to the allocation of these animals with the Mollusca on account of the symmetry of the reproductive organs, we think they are of small importance, even if double : and who can say that the symmetrical Patelloida have not in this respect a similar structure ? but these points are doubtful. M. Deshayes says, " Quoique nous ayons fait des anatomies minutieuses d'Oscabrions, il nous a ete impossible de trouver la seconde issue des organes de la generation ;" and M. Cuvier observes, they became so attenuated that he confessed he could not trace them. Our own researches lead to doubts of these appendages being oviducts ; at the same time we admit, they may prove to exercise those functions : they are situate in the immediate vicinity of the heart and auricles, and may be glands to secrete a liquor for those organs, or the fecundating pouches of the peculiar hermaphroditism of this tribe; in which latter case, the true issue for the ova will probably be R 242 found between the rectum and the posterior part of the ovarian sac. It has heen said that the body is subannulate : in a hundred dissections we could not see much trace of such configuration, or breaks in it to correspond with the segmental arrangement of the valves ; only slight marks, the eifect of pressure, were observed. The connection of the Chitons with the Crustacea is, I think, so very slight and remote as to require no further notice. Having cursorily disposed of certain objections, we will proceed to state our own views, and in their course, allude to other objections and discrepancies. Though the Chitons are in closer alliance with the Bivalves, anatomically, by the arrangement of the circulatory apparatus, symmetry of the branchiae, and by the absence of tentacula and eyes, than by the external hard parts; still in them, there are points of coherence which are not without their value : for instance, in Pholas dactylus, which it almost immediately follows in our method, though the bivalve portion is not broken into regular segments, there are certain testaceous pieces, commonly, though perhaps incorrectly, called accessories, in number six, including the principal valves. We also find in the Chitons a subsymmetrical division into eight segments of what I con- sider essentially an integral patelloid cone, and as much accessorial as those of Pholas; indeed both in one and the other, these component parts are equally necessary and essen- tial. I admit that no great stress ought to be laid on the contrasted points; nevertheless, in conjunction with other decided anatomical analogies, they have their weight in the balance. Our view of the natural position of Chiton is after Dentalium, with which it has marked affinities, and in immediate contact with the Patelloid group, hi which we regard, in almost every respect, Fissurella as the point of comparison, as in it is seen the same form of the cone, though entire instead of broken, the same parity of the branchiae, a similar posterior anal de- bouchure, and the attenuated mantle, gradually thickening, in both genera, to a tumid coriaceous margin, which in Fis- CHITONID^. 243 surella can scarcely be withdrawn within the shell, studded alike in both with papillee and rugosities, and the same mar- ginal fringes. The nervous masses in the two accord closely: the only exception is the striking, but really unimportant, division of the cone of the Chitons into segments; but this incident may be accounted for on very simple grounds. We consider the fracture of the shell not a character denoting an affinity with the Annelida, as the body of the animal has no corresponding articulations, but simply an aid to facilitate locomotion. The foot of the strict symmetrical testaceous Gasteropoda is generally nearly concurrent with the length of the body, and forms its base, from which, by a gradually increasing cone, the animal becomes at maturity fixed to the summit of the shell by a powerful muscle : this structure united to an entire cone, and combined, as in the Bivalves, with the depressing effects of a complete hermapliroditism, that of Venus sine concubitu, almost extinguishes the loco- motive functions ; and we see throughout the Patelloid tribe, all of which have a foot co-extensive with the body, an almost entire fixation to the same spot ; indeed we believe that some of the PateUce pass their existence in the depressions of the rock on which they are cast as embryos, and the same apathy exists in Pileopsis and Calyptrcsa. But nature has judged fit to give the Chitons additional motive powers, for when fixed on the area of a smooth pebble, they will travel off it, whilst the Patella are immoveable : this is owing to the integrity of the cone, and the enormous muscle which fixes the animal to its apex. This structure does not permit the body sufficient flexibility for much progression, and almost confines it to a vertical elevation and depression; but the Chitons, by the segmental condition of their shells, have accorded to them sufficient flexibility to obtain a vermicular motion, and its consequence, a greater facility of march. The Trachelipoda have infinitely superior attributes for motion, from the foot being fixed to a small portion of the body by an elastic cylindrical pedicle that affords a perfect pliability, and the acquisition of the necessary undulatory quality to effect a comparatively facile progression. R2 244 CHITONID^E. The above remarks perhaps furnish us with the proper value of the arguments of malacologists in favour of the Chitons being, by the peculiar disposition of the testaceous covering, allied to the Articulata. It is scarcely necessary to observe, that the usual single powerful muscle of attachment of the animal to the shell in the Patelloid tribe, is in Chiton, from a necessity arising from the disunited structure of the cone, converted into a minuter series of coordinate muscles to attach it and each section of the shell in its proper position. It will now be convenient to look at the anatomy of these animals, of which the most important feature are the medul- lary masses, and for an account of them we refer to the descriptive notes on Chiton fascicularis, in which will be seen the unmistakeable cesophageal collar of the Mollusca, without a trace of the longitudinal knotted or ganglion ic cordon of the Annelida, or any of that division of the Articulata termed Crustacea, including the Cirripoda. This point alone is, perhaps, decisive of the question at issue. The next consi- deration are the organs of the circulation ; these, by being disposed on a mesial line, dorsally, and more externally than in the strict Gasteropoda, have a greater alliance with the conchiferous type ; and as they exhibit some unusual varia- tions in their composition, it will be necessary to examine with detail the extraordinary, I believe unique, structure of these organs, and I hope to arrive at such probable con- clusions as will account for the rationale of this abnormal disposition. The posterior position of the motive power of the circulation will, I think, assist in solving this problem, and must always be kept in view. If we divide the longitudinal area of the animal into eight equal sections, the heart will be found near the hinder extre- mity, and may be considered as composed of two inflations connected by an intermediate marked strangulation; but between them, there is an isochronal systole and diastole action ; the anterior inflation is of an elongated oval shape, and the largest; the posterior is considerably smaller and CHITONID.E. 245 more subrotund. The auricles receiving blood from the bran- chial veins communicate in the usual lateral manner with the greater division of the heart, and at this point present their largest calibre ; they then form an attenuated arcuation on each side the constricted portion, and effect a second contact at the sides of the lesser inflation, which may be regarded as an aortic ventricle receiving the blood by a special