250 



MUSEUM OF ANIMATED NATURE. 



[Limpets, 



species as are long affixed to one spot can obtain 

 this aliment: they must derive their nourishment 

 from the animal and vegetable particles with which 

 the Mater is abundantly charged. 



Those who have been in the habit of observing 

 limpi'ts on the rocks of our own coast cannot fail 

 to have observed that in many instances the shell is, 

 as it were, let into the rock to some depth, and that 

 evidently by the operation of the mollusk in exca- 

 vating a cavity which is adauted precisely to the 

 form and siie of the shell. It is not very easy to 

 explam, in a satisfactory manner, the mode by which 

 this wearing of the rock is accomplished. Some are 

 inclined to attiibute it to the efFect of absorption; 

 others to the perpetual action of a current of water, 

 caused by the action of the branchial fringe around 

 the mantle ; and others to the agency of some se- 

 cretion liy which the structure of the rock is decom- 

 posed. 



Some species adhere to shells, and the same effect 

 is produced as on the rock. 



In an admirable paper in the 'Philosophical 

 Transactions' for 1833, on the economy of mollus- 

 cous animals, Mr. Gray, speaking of a foreign spe- 

 cies (the Patella cochlea), often found at the Cape 

 of Good Hope, states that it lives " almost ex- 

 clusively attached to a large species of ihe same 

 genus, on the surface of which it forms a flat disk 

 exactly the size of its mouth. To form these flat 

 disks (of which there are generally two — one on 

 each side of the apex of the larger Patella, so as 

 almost to form a character of Ihe species), and to 

 assist in the increase of its size, the animal appeara 

 also to absorb the coi-alline or other similar sub- 

 stances with which the larger shells are abundantly 

 covered. The common Patella of our own coast, 

 when long adherent to another shell of its own 

 species, to chalk, or to old red sandstone, or lime- 

 stone, also forms for itself a deep cavity of the same 

 form as its shell, and evidently produced by the dis- 

 solution of the surface to which it is affixed." 



It is a remarkable fact that the limpet adapts the 

 rim of its shell to the shape or ii-regularities of the 

 substance to which it adheres. This has been often 

 noticed, and is dwelt upon by Mr. Gray. He ob- 

 serves, that, " when a Patella or a Crepidula has 

 attached itself to the flat surface of a rock, or the 

 leaf of a large fucus, the base of its shell is flat, and 

 its mouth roundish ; when it adheres to a concave 

 surface, such as the cavity of an old shell, the base 

 becomes flattened, and convex internally ; and when 

 it fixes itself on the round stalk of a fucus, the sides 

 become compressed so as in some measure to clasp 

 the stem, and the lateral portions of the base pro- 

 ject beyond the front and hinder parts to such an 

 extent that when placed on a flat surface it rocks 

 backwards and forwards. Several nominal species 

 of these and allied genera depend on variations in 

 the shape of the shell, caused by the adhesion of the 

 animal to surfaces of different forms : thus the Patella 

 pellucida of Montagu is synonymous with the P. 

 caerulea of the same author, the former having been 

 founded on specimens taken from the stalk, and the 

 latter on individuals obtained from the flattened 

 frond of the fucus, on which the species usually takes 

 up its abode. It is indeed by no means rare to find 

 specimens in which the animal has moved from one 

 of these positions to the other, and in such cases the 

 shell represents P. caerulea, and the base P. pellu- 

 cida, or vice versa. The same change takes place 

 with regard to P. miniata and P. compressa. I have 

 in my collection a specimen of this latter shell, which 

 is P. miniata at the top, it having in its youth lived 

 on the frond of a large Cape fucus ; it afterwards 

 removed to the stem, and liecame compressed, and 

 consequently is in this part the P. compressa ; but 

 by some accident it was again induced to change its 

 situation, and, removing to a flat surface, the edge 

 of the mouth expanded, and it became a second time 

 P. miniata, or perhaps what may be called by some 

 authors P. saccharina, as this also appears to be a 

 conical variety of the same species. Lamarck has 

 described a similar specimen ; and Mr. Sowerby, in 

 his 'Genera of Shells,' has figured an example of 

 this species, showing the two states. In like manner 

 the Crepidula porcellana, when applied to a flat 

 surface, nas an expanded base and a flattened inner 

 lip ; but when adherent to a convex body, such as 

 the stem of a sea-weed, or, as frequently happens, to 

 the back of another shell of the same species, the 

 animal being pressed into the cavity, the inner lip 

 becomes concave, and the sides of the aperture are 

 contracted. In this state the shell is called by some 

 authors C. fomicata. 



" When the shells of this family are adherent to 

 irregular surfaces, they adapt their margins to the 

 irregularities with which they meet. I have several 

 specimens from the coast of Devonshire, ha\ing one 

 or more processes on their sides which fitted into 

 holes in the rock to which I found them attached ; 

 and such changes are the more remarkable, as some 

 specimens are seen constantly moving from place to 

 place, whilst others appear to remain for a long time 



fixed to one spot, and even those that are stationary 

 in the young state constantly elevate the margins of 

 their shells when the tide is low." 



From this circumstance it is evident that many 

 varieties of these shells may be mistaken for distinct 

 species, of which indeed the catalogue is very 

 extensive. To this |)oint Mr. G. B. Sowerby 

 (' Genera of Shells') has made express allusion, and 

 adduced some instances in which such a mistake 

 mieht very pardonably be made. 



From these preliminary observations we proceed 

 to notice a few examples, each the representative 

 of one of those subgeneric groups founded by M. 

 de Blainville on external configuration. 



Section o. This group is composed of such spe- 

 cies as have a nearly true conical form of shell, 

 with the apex obtuse, vertical, and almost exactly 

 mesial. 



2838.— Thb Couuoh Limpet 



(Patella vulgata). This species is abundant on the 

 coasts of Europe, and few have visited the rocky 

 shores of our island without having noticed it, if, 

 indeed, they have at all attended to the living pro- 

 ductions of the sea, which many who visit what are 

 termed watering-places never even dream of. Many 

 an hour which drags heavily with the ennuyfi would 

 pass agreeably were such objects sought after and 

 observed ; but sorry are we to say that to some Na- 

 ture has little attraciiveness, little to interest or de- 

 light. Such a man exists as though he existed not, 

 — he loses half the pleasures allotted to human en- 

 joyment. 



Section /3. In this section the species are less 

 conical, and the apex is placed more anteriorly, with 

 a slight inclination forwards. 



2839.— The Gilded Limpet 



(Patella deauiata). This species is found in the 

 Straits of Magellan, or Mageihaens, on the shores of 

 the Falkland Isles, &c. 



Section y. In this section the species are elon- 

 gated, oval, and compressed at the sides, with the 

 apex anterior, and inclined forwards. 



2840. — The Ccmpressed Limpet 



(Patella compressa). The species is a native of the 

 Indian Seas. 



Section i. In the species included under this di- 

 vision the form of the shell is extremely flat, or de- 

 pressed, and the apex very slightly developed, and 

 somewhat anteriorly placed. 



2841. — Thk Scutellar Limpet 

 (Patella scutellaris). This is a singular form, with 

 an irregular margin, and furrows radiating from a 

 little abrupt conical apex. 



Section i. This contains species depressed like 

 those of the preceding section, but which differ in 

 being much narrower anteriorly than posteriorly. 



2842. — The Spoon-shaped Limpet 

 (Patella cochlearea). The under surface of this ex- 

 ample is represented. It is a type of the genus 

 Helicon of De Montlort. 



Section Z- This section is composed of oval spe- 

 cies, with a well-marked apex, decidedly inclined 

 forwards. 



2843. — The Pectinated Limpet 



(Patella jiectinata). This is a pretty species, found 

 in the Mediterranean Sea. 



Section ij. In this section the species have the 

 shell delicate, oval, nacreous, with a festooned mar- 

 gin ; the apex is marginal, anteriorly. 



2S44. — ^The Boat-shaped Limpet 



(Patella ct/mbularia). This species is so different 

 in the form and appearance of its shell, that, at first 

 sight, it might scarcely be recognized as belonging 

 to the present genus. 



Though the living species of Patella are ex- 

 tremely numerou.', M. Deshayes enumerating a 

 hundred and four, yet the fossil species are very li- 

 mited, and of these one. Patella sequalis, is existing 

 in the seas of Europe ; it is met with, fossil, in the 

 crag. According to Mr. Sowerby fossil forms of 

 Patella occur in the oolite, in the lias, in the Oxford 

 clay, and the chalk marl, of the secondary series ; 

 also in the calcaire grossier, and probably the Lon- 

 don clay of the tejtiary series, together with the 

 crag — the pliocene of Mr. Lyell. 



Before leaving the genus Patella we may notice 

 that termed Scutella by Mr. Broderip, established 

 on some shells collected by Mr. Cuming among the 

 islands of the South Pacific. Unfortunately the 

 living animals had been destroyed before the shells 

 were taken, probably by some carnivorous creature ; 

 but, though proof positive is wanting. Mi-. Broderip 

 is inclined to refer the genus to the Cyclobranchiata. 

 See 'Proceeds. Zool. Soc.,' 1834, p. 47. 



With respect to the genera Siphonaria, Patelloida, 

 and I.ottia, which in the form of the shells closely 



resemble the Limpet (Patella), yet, as the mollusks 

 differ greatly in organization, having a single pec- 

 tinated branchial apparatus on the right side, as in 

 Fissurella, and not a cordon of filaments, they must 

 be referred to the Scutibranchiata, to which order, 

 as we have said, Fissurella and Einareinula belong. 



We now turn to the genus Dentalium, respecting 

 the position of which there is yet no little diffi- 

 culty. 



By the earlier writers the Dentalium was regarded 

 asan annelid, one of the Tubicolir, and even Cuvier, 

 in the last edition of the ' Rigne Animal," retains 

 it among those articulated creatures, observing, 

 however, that the recent observations of M. Sa- 

 vigny, and more particularly of M. Deshayes, ren- 

 der this arrangement very doubtful. He adds, — 

 "The animal does not present any sensible articula- 

 tions, nor any lateral bristles, but it has anteriorly a 

 membranous tube, in the interior of which is a sort 

 of foot, or fleshy conical operculum, which closes 

 the orifice ; on the base of this foot is a small flat- 

 tened head, and on the neck are the branchiir, in 

 the form of tul^s. If the operculum reminds us of 

 the foot in Vermetus and Siliquaria, which have 

 been restored to the Mollusca, the branchiae have 

 much resemblance to those of Amphitrite and Te- 

 rebella. Further observations on the anatomy of 

 Dentalium, and principally on the nervous and vas- 

 cular systems, will resolve the problem." 



It is to M. Deshayes that the discovery of Ihe 

 real nature of the Dentalium is owing, and his opi- 

 nions respecting its being a true mollusk have been 

 fully confirmed. Linnaeus arranged Dentalium after 

 Patella, and before Serpula; and Lang placed it in 

 a group after Patella, together with all the calcare- 

 ous tribes of Annelids then known. Brugiires gave 

 it almost the same position as Linnaeus. 



M. de Blainville, in his ' Malcologie,' 1825, agrees 

 with M. Deshayes in assigning the Dentalium to the 

 Mollusca, and he establishes it as the type of an 

 order, which he terms Cirrhobranchiata, and places 

 next to Patella. M. Hang, in 1829, follows M. de 

 Blainville, but places the Cirrhobranchiata, of which 

 Dentalium is the only representative, between Fis- 

 surella and Patella. Mr. Gray, who has compared 

 the description of the animal given by M. Deshayes 

 with specimens in Ihe British Museum, is inclined, 

 we believe, to consider its place in systematic ar- 

 rangement as approximating to the Fissurellae, but 

 yet at a considerable distance. With respect to the 

 British species Mr. Gray observes, that the apices 

 often appear to be broken or worn off, and that the 

 animal, for protection, then forms a slight tube with- 

 in, which is more or less produced beyond Ihe tip; 

 and the late Dr. Turlon described a specimen so re- 

 paired as a distinct species under the name of Den- 

 talium labiatiim. Several specimens of the common 

 Dentalium are now before us, and every one has the 

 tip perfect, and Ihe edges of the small apical orifice 

 are smooth and polished. 



In placing this genus after Patella we do not 

 mean thereby to indicate that such is its true situa- 

 tion ; doubtless it is the type of a distinct family, 

 and perhaps order, for which De Blainville's name 

 of Cirrhobranchiata is very appropriate. 



The shell in Dentalium is very simple ; it is an 

 elongated cone, slightly curved, and open at each 

 extremity by a rounded orifice. 



The animal is of a conical elongated form, the dor- 

 sal surface corresponding with the convexity of the 

 shell, the ventral suiiace with the concavity. The 

 whole anterior part of the animal is invested by a 

 fine membrane, which is fixed posteriorly to the 

 origin of the foot, and is free in front where its cir- 

 cumference is thickened. It is perforated in the 

 centre; Ihe thickened portion is muscular. Dividing 

 this mantle down the middle surface of the back, the 

 foot, head, and branchiae are brought to view. The 

 foot is elongated, subcylindrical, slightly conical, 

 and fleshy. The head consists of a mouth only, 

 and is situated superiorly at the hinder extremity 

 of the foot. The respiratory system consists of two 

 branchiae symmetrically situated on the lateral and 

 posterior parts of the neck, and supported on a 

 divided peduncle. They are composed of many 

 very fine, soft, flexible, tentacular filaments, with 

 club-shaped terminations, and appear from their 

 position to be equally adapted for directing nutri- 

 ment towards Ihe mouth, and for fullilling the task 

 of aerating the blood. 



The form and characters of Dentalium will be 

 better understood by reference to our pictorial spe- 

 cimens than by a long verbal description. 



Fig. 2845 represents the shell and animal of Den- 

 talium entalis: a, the shell of Dentalium eiitalis, of 

 the natural size; ii, the shell magnified and broken 

 lonsjitudinally, showing ihe animal in a contiacted 

 state ; a, the' posterior extremity prolonging itself 

 into a small accidental tube; c, the shell magnified, 

 with Ihe animal at the moment of its advancing out 

 in order to obtain food ; a and /;, the foot, the lobes 

 of which are developed in the form of a corolla; c, 

 a part of the collar of the mantle. 



