MOLLUSC A. 



25 



Subdivision II. 



Fresh water shells covered with a spurious epidermis, and 

 having lateral teeth. 



Cyclai cornea. PI. 60. f. 50. Animal provided with a double 

 united tube at the posterior termination of the cloak, foot 

 long, and powerful for the size of the animal. 



Piscidium obliquum. PI. 60. f. 51. 



SECTION III. TENUIPEDES. 

 FAMILY I. NYMPHACBA. 



Shell never havinjj more than two primary teeth in each 

 alve; frequently gaping atits lateral extremities ; ligament ex- 

 terior. The foot of the animal is small, and often compressed ; 

 the species all inhabit the shores of the sea. 



Donax truncvlus. PI. 60. f. 46. The animal has two long 

 slt'inier tubes, which are received into a sinus of the mantle ; 

 and provided with a broad foot. F. 47. The right valve 

 removed, a a, the adductor muscles ; A, the foot ; s s, the 

 right lip ; m n, the two lobes of the branchiae ; bd,ce, the two 

 trachea' ; the left vein is at i. 



Tellina planata. PI. 60. f. 97. 



FAMILY II. LITHOPHAGI. 



The shells gape more or less at their anterior side ; ligament 

 exterior ; they bore into rocks and clay, without the aid of 

 accessory shells, but by what means naturalists have not yet 

 discovered. 



Fenerupis irus. PI. 60. f. 69. 



FAMILY III. CORBULACEA. 



Shell inequivalve, with the ligament placed interiorly. 

 Pandora rostrata. PI. 18. f. 72. 



FAMILY IV. MACTRAC.EA. 



Shell equivalve, frequently gaping at the lateral extremities ; 

 ligament placed interiorly, or partly exteriorly ; animal with 

 the foot small and compressed ; the tubes are united and short. 



Mactra Neapolitana. PI. 60. f. 40. b c, the trachsea; d. the 

 foot. 



SECTION IV. CRASSIPEDES. 



The mantle, either entirely or in part united before the foot, 

 thick, placed posteriorly ; the shell gaping when shut 



FAMILY I. MYARIA. 



Shell with a broad spoon-shaped tooth in each valve, or in 

 one only, and gaping at both lateral extremities, or at one 

 only ; ligament placed interiorly. Live sunk in ooze or sand. 



Mya arenaria. PI. 60. f. 45. The mantle opens at the ante- 

 rior extremity, or near the middle only, for the passage of the 

 foot, and extended from the other end with a double tube 

 which projects from the shell, whose extremities are always 

 gaping ; the double tube forms a fleshy cylinder. 



FAMILY II. SOLENIDES. 



Shell transversely elongated, without accessory pieces, and 

 gaping at the lateral extremities only ; ligament placed exte- 

 riorly ; the foot issues from the anterior extremity or from 

 that side in which the teeth are nearest. 



Solen Vagina. PI. 60. f. 96. The foot of the animal is conical, 

 which enables it to burrow with great facility in the sand, e, 

 the trachiae ; k, the cloak ; n n, adductor muscles ; the foot, b c. 



FAMILY III. PHOLADARIA. 



Shell bivalve, with accessory pieces to the valves ; they gen- 

 erally gape much anteriorly. The whole family are borers. 



Pholun rldi'tylus. PI. 60. f. 95. The mantle is reflected exter- 

 nally upon the hinge, where it sometimes contains two or three 

 supernumerary calcarious bodies; the foot issues through the 

 aperture on the side next the mouth, where it is widest, and 

 from the opposite one project the two tubes, which are united 

 and susceptible of inflection in every direction. F. 89 shows 

 the adductor muscle of the pholas. 



FAMILY IV. TDBICOLA. 



Shell contained in a testaceous sheath, distinct from its 

 valves, incrusted entirely or in part in the wall of this tube, or 

 projecting outwards. 



Teredo navalis. PI. 60. f. 16. The mantle extended in a 

 tube much longer than the two small rhomboidal valves, and 

 terminated by two short tubes, the base of which is furnished 

 en each side with a stony and movable operculum. These 

 acephala, while quite young, penetrate and establish their 

 habitations in submerged pieces of wood, such as piles and the 

 bottoms of ships ; completely destroying them in a very short 

 space of time, a, the fflsophagus, which is very short, and lies 

 on the left side of the neck ; the canal swells out, and becomes 

 a stomach, 6, which, in its external appearance, is a large bag. 

 extending the whole length of the cavity of the abdomen, but) 



when laid open, it is found to have a septum, c, dividing it 

 longitudinally into two equal cavities, except at the lowest 

 part, where they communicate atrf, the septum being wanting. 

 The intestine has its origin close to the termination of the o>so- 

 phagus, is extremely small, dilates into a cavity containing A 

 hard, white spherical body, the size of a pin's head, and then 

 makes a turn upon itself. The course it follows is shown by 

 t hi) letters e e. 



CLASS CIRRIPEDA. 



Following ttie general practice, we treated the coverings of 

 the Cirripeda as a branch of Conchology ; and we now proceed 

 with the plan we adopted in following up Mollusca, by the 

 characters of the animals which inhabit the testaceous Cirri- 

 peda. 



The Cirripeda form an intermediate group between the 

 Mollusca and Articulata. The bodies are enveloped in a mantle, 

 and testaceous plates or valves, which are nearly allied to those 

 of the Acephala. The mouths of the animals are provided with 

 lateral jaws, and the abdomen with filamentary jointed pro- 

 cesses, named cirri, arranged in pairs, composed of numerous 

 little ciliated articulations, and corresponding to feet or fins, 

 similar to those which exist under the tail of crustaceous ani- 

 mals. Their heart is situated in the back, and the branchiae 

 emanate from the sides ; the nervous system forms a series of 

 ganglions, on the lower part of the abdomen. These cirri, 

 however, may be considered as analogous to the articulated 

 appendages of some species of Teredo, while the ganglions are 

 in some measure repetitions of the posterior ganglion of the 

 bivalve Mollusca. The position of these animals in the shell is 

 such, that the mouth is at the bottom, and the cirri near the 

 orifice. Between the last two cirri is a long fleshy tube, that 

 has sometimes, but erroneously, been taken for their proboscis, 

 and at the base of which, near the back, is the anal opening, 

 Internally, a stomach is found inflated by a multitude of small 

 cavities in its parietes, which appear to fulfil the functions of a 

 liver, a simple intestine, a double ovary, and a double serpen- 

 tine oviduct, whose walls produce the prolific fluid, and 

 which, prolonged in the fleshy tube, open at its extremity. The 

 animals of this class are incapable of locomotion, being always 

 fixed. This class was all ranked under a single genus by Lin- 

 naeus, by the title of Lepas. Brugieres divided them into 

 two, and Lamarck has subdivided them still farther, at the 

 suggestion of Dr Leach, and they now form a class of them- 

 selves. 



The animals of this class are always protected by a multi- 

 valve shelly covering, which is composed of a number of separ- 

 ate pieces ; these are connected by a membrane in the pedun- 

 culata, and those of the setsiliasnt in number are articulated 

 at their sides, and kept together from their base, being attached 

 to a calcarious plate, which is firmly attached to some ex- 

 traneous substance. These last form a conical covering, open 

 at the top, which is protected by an operculum or lid, composed 

 of four pieces. 



The first order of cirripeda have but five- valves, and these 

 are placed on the summit of a tubular, membranous peduncle, 

 varying in length in different species. In one genus, besides 

 the five principal valves, other smaller ones are found, which 

 are termed accessory valves. All the animals are hermaphro- 

 dite and marine. 



The characters of the class are, soft animals, destitute of 

 head and eyes, covered with a plurality of shells, and always 

 fixed to a certain spot ; the bodies are inarticulated, provided 

 with a mantle, tentacula, and cirri ; arms issuing from above, 

 and many-jointed. 



ORDER I. PEDUNCULATA. 



The body compressed, and supported on a tubular peduncle. 



Otion Cuvieri. PI. 19. f. 26. Body pedunculated, ventricose 

 above, and enveloped in a membranous tunic ; two lobes dis- 

 posed in the form of horns directed backwards, open at their 

 extremity, truncated and placed at the summit of the tunic ; 

 having a lateral opening with many articulated arms or feelers. 



Cinerat mttata. PI. 19. f. 27. Body seated on a peduncle, 

 enveloped in a membranous tunic, with an anterior opening 

 situate below the summit, and numerous slender, articulated 

 arms. 



Potticipes mitella. PI. 19. f. 28. Body resting on a tubular, 

 tendinous tubercle, with many tentacular arms. 



Anatifa vitrea. PI. 19. f. 30. With a compressed mantle, 

 open on one side and supported on a tubular tendinous pedun- 

 cle ; it has twelve pair of ciliated cirri or arms, six arising 

 from near the summit on each side, those nearest the mouth 

 being the thickest and shortest; the branchiae are elongated 

 pyramidal appendages, that adhere to the external base of the 

 whole of the cirri or part of them. 



ORDER II. SESSILIA. 



Body destitute of a peduncle, and inclosed in a shell of vari- 

 ous parts, fixed immovably by its base, with a testaceous lamina 

 to extraneous marine bodies ; the mouth at the upper and an- 

 terior part of the body. In the interior of the opening is placed 

 an operculum formed of two or four movable pieces, which 

 the animal opens in the centre while projecting Us tentacular 



Pyrgoma crenata. PI. 19. f. 31. Operculum bivalve. 



