ACEPHALA TESTACEA. 411 



which transmits the foot, is not much larger. Some species are 

 found in the Mediterranean. 



There are also several that are fossil(l). 



DicERAs, Lam. 



Between Diceras and the Chamae there is no essential differ- 

 encej the cardinal tooth of the former is very thick and the spiral 

 lines of the valves are sufficiently prominent to remind us of two 

 horns(2). In the 



IsocARDiA, Lam., 



We observe a free, regular, and convex shell, with spirally curled 

 summits, divided anteriorly. The animal, — Glossus, Poll, — only 

 differs from that of an ordinary Chama in having a larger and more 

 oval foot, and because the anterior opening of its mantle begins to 

 resume its ordinary proportions. 



A large, smooth, red species, the Chama cor, L. ; Chemn., 

 VII, xlviii, 483, inhabits the Mediterranean(3). 



FAMILY IV. 



CARDIACEA. 



The mantle is open before, and there are, besides, two 

 separate apertures, one for respiration, the other for the 

 fiEces, which are prolonged in tubes, sometimes distinct, and 

 at others united in one single mass. There is always a trans- 

 verse muscle at each extremity, and a foot generally used for 

 crawling. It may be considered as a general rule, that those 

 which are furnished with long tubes, live in ooze or in sand. 

 This mode of organization may be recognized on the shell by 

 the more or less depressed contour described by the inser- 



(1) See the Conchiol. Foss. Subap., of Brocchi, and the Coq. Foss. des Env. 

 de Paris of M. de Lamarck. 



(2) Fossil shells from the Jurassic strata. Die. arietina. Lam. de Saussure, 

 Voy. aux Alpes, I, pi. ii, f. 1 — 4. 



(3) Add Ch. moltkiana, Chemn., VII, xlviii, 484 — 487- 



