CHITONELLUS. MbLLUSCA. 67 



longitudinal series of testaceous, imbricated, transverse, and 

 moveable plates ; head anterior, sessile, with the mouth be- 

 low ; no tentacula or eyes ; branchiae disposed around the 

 body, under the margin of the skin ; anus at the posterior 

 extremity. 



The Chitons crawl upon their foot or fleshy disk, and are attached to rocks and 

 stones like the limpets. They are found along the coasts at no great depth. 



C. gigas, Gmel. Shell with eight thick convex valves, the first 

 valve crenated, the last toothed, and the intermediate ones en- 

 tire ; colour white, with a blackish-brown coriaceous margin. 3 

 to 4 inches long. Inhabits coast at Cape of Good Hope 

 Chem. viii. pi. 96, fig. 819. 



C. marginatus, Gmel. Shell with eight carinated valves, and a 

 serrated reflected margin ; colour dusky-brown or reddish. ^ inch 



long. Inhabits coasts of Britain, &c. Common. B Browns 



Illust. pi. 35, fig. 3. 



C.fascicularis, Lin. Shell with eight valves, and a lateral tuft of 

 hair on each ; colour cinereous ; back slightly keeled. ^ inch 

 long. European coasts. B Brown s Illust. pi. 35, fig. 5, 8. 



Gen. 22. CHITONELLUS, Lam. 



Body narrow, elongated, with the middle of the back furnished 

 in its whole length by a multivalve shell ; sides naked ; 

 branchiae disposed round the body ; foot divided longitudi- 

 nally by a deep furrow. 



C. Icevis, Lam. Shell with the valves smooth, and the margin en- 

 tire ; the last joint behind mucronate, and the first before round- 

 ed, and broader than the others. 1J inch long. Inhabits coasts 

 of New Holland. Law. vi. 1. 317. 



Gen. 23. PHYLLIDIA, Lam. 



Body oval oblong, slightly convex above ; dorsal skin coriace- 

 ous, varicose or tubercular, forming a projecting margin 

 around the body ; branchiae disposed under the margin of 

 the skin in a series of transverse leaflets ; tentacula four ; 

 orifices for generation on the right side ; anus dorsal and 

 posterior. 



P. varicosa, Lam. (P. trilineata, Cuv.) Body oval elongate ; back 

 blackish, with three longitudinal subnodose yellow varices. In- 

 habits Indian seas. An. Mus. v. pi. 18, fig. 1-6. 



FAMILY VII. TUITONIACEA. 



Branchiae exterior, placed above the mantle on the back or 

 sides ; respiring in water. 



This family are distinguished from all the other Gasteropoda by the situation of 

 their branchiae, which are exterior. In many genera these branchiae appear to be 

 a degeneration of the mantle, or that they are formed by portions of this covering 

 having become branchial. Their body is elongated, naked, and without a shell, ei- 

 ther internal or external. They are all marine. 



