412 MOLLUSC A. 



tion of the edges of tlie mantle previous to its uniting with the 

 impression of the posterior transverse muscle(l). 



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, 8cc. Ribs, more or less elevated, are regularly 

 distributed 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 elbow in the middle and with its point directed forwards, and 

 two short or but moderately long tubes. 



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

 some of which arc 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 Hemicardium, we might separate those spe- 

 cies in which 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 configuration(2). 



DoNAX^ Lin. 



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

 their shell is of a very different form, being a triangle, of which the 

 obtuse angle is at the summit of the valves, and the base at their 

 edge, and of which the shortest side is that of the ligament, or 

 the posterior side, a rare circumstance in this degree, among bi- 

 valves. They are generally small, and prettily striated from the 

 summits to the edges; their animal — Peronjea, Poli, is furnished 



(1) They form the family of the Conchacea, Blainv. 



(2) Cardium cardissa, VI, xiv, 143— 146; — Card, roseum, lb., 147; — Card, mon- 

 strosumy lb. 149, 150; — Card, hemicardium. Id., xi, 159 — 161. 



The other Cardia of Gmelin may remain where they are, the C. gaditanum ex- 

 cepted, which is a Pectunculus. There are several fossil species described by 

 Messrs Lamarck, Brocchi, and Brongniart. 



