ORDER T E C T I B RAN C H I AT A. COVERED-GILLS. 



133 



ILLUSTRATIVE EXAMPLES. 



PLATE 5. 



APLYSIA (also written, though not so correctly, Laplysia). A shell 

 horny, transparent, and in form of a shield, placed horizontally on the back, 

 its convex side being uppermost. Body not divided ; head supported by a 

 neck ; tentacula four, two hollowed-like ears, and having the eyes at their 

 base, the other two tentacula flattened ; they sometimes have membranes 

 proper for swimming ; mouth a vertical slit, having two lateral subcorneous 

 labial plates ; branchia in the form of a plume, placed in a dorsal cavity, 

 and protected either by a free operculum at the right side, or by the ap- 

 proximated edges of the mantle. 



The species of Aplysia are found in the Mediterranean, European and 

 West Indian seas; some are also found in our own seas. The name is 

 derived from a limpid liquor which it exudes when disturbed ; and on 

 account of a fancied resemblance between its appearance and that of a hare 

 crouching, it was called by the ancients Lepus martinis, or sea-hare. This 

 animal, which has considerable general external resemblance to the Slugs, 

 has a long narrow foot, from the front of which projects the head. The 

 development of the lateral borders of the foot is very great, so that they lap 

 over each other at the animal's will, on the dorsal surface of the body, upon 

 which is also a large semicircular valve-like piece of skin, including muscle, 

 arising from its left side only, and often forms a sort of canal, leading the 

 water to the branchial apparatus, which, like the lid of a basket, it almost 

 conceals, and hence arises the arrangement of this and similar animals in the 

 Tectibranchiate Order of Gasteropoda. 

 Illustration : Aplysia punctata. 



PLEUROBRANCHUS (the Lamellaria of Montague). The animals of this 

 genus have an oval, fleshy body, covered by the mantle, which is strength- 

 ened by a thin, expanded, subspiral shell, flattened obliquely ; foot broad, 

 equally margined ; tentacula two, cleft longitudinally on the outside ; mouth 

 anterior, placed below, resembling a proboscis ; branchia? on the right side, 

 situated in a canal. 



Type of the genus, Butta plumula. Four or five species, of which two 

 are found on the southern coast of England. 



Illustrations : Pleurobranchus Peronii, Lamellaria memhranacea. 

 DOLABELLA. Body creeping, oblong, narrowed in front, club-shaped, 

 and enlarged behind, end obliquely truncated, so as to leave an oblique 

 orbicular plane ; edge of the mantle plaited, and lobed on the back ; tenta- 

 cula four ; half tubular, placed in pairs ; lid of the gills, enclosing the shell, 

 covered by the mantle, and placed near the hinder part of the back ; anus 

 dorsal, placed behind the gills, in the middle of the orbicular dorsal face. 

 Shell oblong, slightly arched, somewhat ear-shaped ; front narrow, thick, 

 callous, and somewhat spiral ; the other end broad, flattened, thin, and 

 rounded at the edge. 



The Dolabellce are most nearly allied to the Aplysice, but they differ from 

 the latter in the animals being destitute of fin-like expansions, and in the 

 shape of the body, and in the shell being solid and calcareous, instead of 

 horny and flexible, as in the latter. They are stationary, and often form for 

 themselves a kind of cylindrical tube from the sand and slush of the sea- 

 shore. They are all found in the tropical seas. 



The species D. Peronii is three or four inches long, and the whole body 

 covered with small fleshy tubercles. They are very difficult to be seen on the 

 shores, for they bury themselves a little depth in the slush. 



In the D. Icews the skin of the animal is quite smooth, and the shell 

 nearly membranaceous. 



Illustration : DolabeUa Rumphii. This species was figured by Rum- 

 phius, hence its name : it is most probably from the Molucca Islands. 



NOTAECHUS. The species resemble in many respects those of Aplysia. 

 They have not, however, a cloak ; their lateral crests are united and cover 

 the back, leaving merely a small dorsal slit or fissure, which is in some 

 oblique, to conduct the water to the branchiae, which are very long ; foot 

 long and narrow ; operculum either rudimentary or wanting. 

 Illustration : Notarchus Cuvieri. 

 ACERA. Shell (in those which have one) exceedingly light and horny, 



more or less convolute, oblique, wanting a visible spire, few whorls, and too 

 small to contain the animal. Branchiae covered with a cloak; tentacula 

 short, bent, and widely separated, forming together a sort of fleshy buckler, 

 beneath which the eyes are placed ; mouth, crescentrshaped, destitute of 

 sinus or canal. 



Illustration : Acera carnosa. 



BULL.EA. The animal of this genus scarcely differs from that of the genus 

 Bulla. The shell is more considerably enveloped in the substance of the 

 cloak, and there is no muscle of attachment. It is more open, much less 

 convex externally, and is but very slightly involuted. There is only one 

 species, Bidla aperta of former authors ; and there appears scarcely sufficient 

 reason for the separation which Lamarck has made. This animal possesses, 

 in common with Laplysia (Aplysia), the property of ejecting a liquor, when 

 it is alarmed or touched, which tinges the fingers of a blood colour. It is 

 not an uncommon inhabitant of the British coast. 

 Illustration : Bulla aperta. 



BULLA. Body ovate oblong, rather convex, divided above into two 

 transverse portions; the cloak folded behind; head scarcely obvious; no 

 apparent tentacula ; branchiae dorsal, posterior covered by the cloak ; anus 

 on the right side ; the hinder part of the body covered by a shell which is 

 attached by a muscle ; shell univalve, ovate-globose, convolute ; no columella, 

 no external spire ; aperture the length of the shell ; the external margin acute. 

 There are several circumstances in the structure of the animals of this 

 genus which give them a considerable relation to Aplysia. From the more 

 important points of affinity, however, which exist between this genus, 

 Buttcea, and Acera, Lamarck has formed them into a distinct family under 

 the name of BuLleens. The stomach consists of two large flattened testa- 

 ceous pieces, which, with a smaller one, and united by a strong muscular 

 structure, serve the office of a gizzard in comminuting the food for digestion. 

 The shells of different species of Bulks differ remarkably from each other. 

 That of B. Ugnaria is very solid and testaceous, and finely coloured ; that of 

 B. acera, on the contrary, is so thin as to be perfectly elastic, and semitran- 

 sparent, is of a uniform horn colour, and appears scarcely to possess a trace 

 of carbonate of lime. 



De Montfort has made a distinct genus of B. Ugnaria, to which he has 

 given the name Scaphander. 



Illustrations: Butta Ugnaria, Bullina Guianensis. 



UMBELT.A. Body very thick, oval, and furnished with a dorsal shell ; 

 foot very large, smooth, and flat beneath, everywhere projecting, cleft in 

 front, and attenuated behind ; head indistinct ; mouth at the bottom of a 

 funnel-shaped cavity in the anterior cleft of the foot ; two pairs of tentacules, 

 the upper posterior pair closely approximated, thick, short, truncated, and 

 cleft throughout their whole length, the interior of the cleft filled with 

 transverse folds ; the anterior pair very delicate, broad, in shape of a cock's- 

 comb, supported each by a pedicle on the sides of the mouth ; branchial 

 organs foliaceous, disposed in form of a long cord, occupying the whole of 

 the anterior and right side of the groove of separation, between the foot and 

 the mantle, and at its hinder end is the vent; shell exterior, orbicukr, 

 somewhat irregular, depressed, or quite flat, its upper surface scarcely 

 distinguished by a very minute tip ; edges sharp ; internal surface slightly 

 concave, and presenting a callous disc, indented centrally, and encircled with 

 a smooth limb. 



The examination of the Mollusc belonging to this shell has been made by 

 Blainville, who, as is his usual practice, changed the name of the genus, and 

 applied to it that of Gastroplax, for Patella Umbetta, the Chinese Parasol 

 Limpet, because the specimens of the animal in the British Museum had 

 the shell (accidentally) cemented to the under side of the foot. Lamarck, 

 in his History, first corrected the error, by some drawing of the animal 

 which he had seen, and the fact has been verified by examining the Museum 

 specimen, which has been figured for the first time in the Plates of this 

 Work, under the name of Umbella Indica. Two species are described, 

 one from the Indian seas, U. Indica, Lam. ; Patella Umbellata, Gmel. ; and 

 the other from the Mediterranean, U. Mediterranea, Lam. 

 Illustration : Umbella Indica. 



