581 



SUPPLEMENT. 



SECTION IV. CRASSIPEDES. 



The mantle, either entirely or in part united before 

 the foot, thick, placed posteriorly ; the shell gaping when 

 shut. 



FAMILY I. MYAKIA. 



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. 24, f. 45. 



FAMILY II. SOLENIDES. 



Shell transversely elongated, without accessory pieces, 

 and gaping at the lateral extremities only ; ligament 

 placed exteriorly ; the foot issues from the anterior ex- 

 tremity or from that side in which the teeth are nearest. 

 Solen Va<iina, pi. 24, 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, the ad- 

 ductor muscles; the foot, b c. 



FAMILY III. PHOLADARIA. 



Shell bivalve, with accessory pieces to the valves; 

 they generally gape much anteriorly. The whole fa- 

 mily are borers. Plwlas dactylus, pi. 24, f. 95. f. 89, 

 muscle of do. 



FAMILY IV. TCBICOLA. 



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. 

 24, f. 16. 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 

 oesophagus, which is very short, and lies on the left side 

 of the neck ; the canal swells out, and becomes a stomach, 

 b, which, in its external appearance, is a large bag, ex- 

 tending 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 at d, the 

 septum being wanting. The intestine has its origin 

 close to the termination of the oesophagus, 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 

 the letters e e. 



CLASS CIRRIPEDA. 



The Cirripeda form an intermediate group 

 between the Mollusca and Articulata. The 

 bodies are enveloped in a mantle, and tes- 

 taceous 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, com- 

 posed of numerous little ciliated articulations, 

 and corresponding to feet or fins, similar to 

 those which exist under the tail of crustaceous 

 animals. 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 

 Terredo, 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 itsparietes, 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 Linnaeus, by the title of Lepas. 

 Brugieres divided them into two, and Lamarck 

 has subdivided them still further, at the sug- 

 gestion of Dr Leach, and they now form a 

 class of themselves. The animals of this class 

 are always protected by a multivalve shelly 

 covering, which is composed of a number of 

 separate pieces ; these are connected by a 

 membrane in the pedunculata, and those of the 

 sessilia six in number are articulated at 

 their sides, and kept together from their base, 

 being attached to a calcareous plate, which is 

 firmly attached to some extraneous 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, mem- 

 braneous peduncle, varying in length in dif- 

 ferent species. In one genus, besides the five 

 principal valves, other smaller ones are found, 

 which are termed accessory valves. All the 

 animals are hermaphrodite and marine. The 

 characters of the class are, soft animals, des- 

 titute of head and eyes, covered with a plur- 

 ality 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,r>\. 33, f. 26. Cineras vittata, pi. 

 33, f. 27. Pollicipes mitella, pi. 33, f. 28. Anutifa vtirea, 

 pi. 33, f. 30. 



ORDER II. SESSILIA. 



Body destitute of a peduncle, and inclosed in a shell 

 of various parts, fixed immovably by its base, with a 

 testaceous lamina to extraneous marine bodies; the 

 mouth at the upper and anterior 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 its tentacular arms. 

 Pynioma crenata, pi. 33, f. 31. Balanus communis, pi. 

 24, f. 94. aa, the ventre; 7nj,the liver; axe, the ovarinm; 

 h, the spermatic ducts; AB, the oesophagus. 



