ACKPHALA TKSTACEA. 



I \MILY IV. 



CARDIACEA. 



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

 apertures, one for respiration, the other for the faeces, which are pro- 

 longed in tubes, sometimes distinct, and at others united in one single 

 mass. There is always a transverse 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 

 l>y the more or less depressed contour described by the insertion of 

 the edges of the mantle previous to its uniting with the impression of 

 the posterior transverse muscle*. 



CARDIUM, Lin., 



The Cardia, like many other bivalves, have an equivalve, convex 

 shell, with salient summits, curved towards the hinge, which, when 

 viewing it sidewise, gives it the figure of a heart ; hence its name of 

 Cardium, heart, &c. Ribs, more or less elevated, are regularly dis- 

 tributed from the summits to the edges of the valves; but what 

 chiefly distinguishes the Cardia, is the hinge, through which, in the 

 middle, are two small teeth, and at some distance before and behind 

 a projecting tooth or plate. The animal, CERASTES, Poli, has ge- 

 nerally an ample aperture in the mantle, a very large foot forming an 

 clhou- in the middle and with its point directed forwards, and two 

 short or but moderately long tubes. 



Numerous species of Cardia arc found on the coast of France, 

 some of which are eaten, such as the 



C. edule, L. ; Chemn., VI, xix, 194. Fawn-coloured or 

 whitish with twenty-six transversely plicated ribs. 



Under the name of H EMI CARDIUM, we might separate those species 

 in \\-hich the valves are compressed from before backwards, and 

 strongly carinated in the middle; for it seems almost certain, that 

 a modification of the animal must be a necessary consequence of this 

 singular configurationf. 



DONAX, Lin., 

 The Donaces have nearly the same kind of hinge as the Cardia, but 



* They form the family of the CONCH ACEA, Blainv. 



t Cardium Cardissa, VI, xiv, 143 146; Card, roseum, Ib., 147 ; Card, mon- 

 strusum, Ib. 149, 150; Card, hcniicttrdium, Id., xi, 159 161. 



Tin- other Cardia of Gmelin may remain where they are, the C. gadittinum excepted, 

 whirh is a IVctunculus. There are several fossil species described by Messrs. Lamarck' 

 Brocchi, and Brongnmrt. 



M 2 



