HEART-SHELLS. | 2a 
FAMILY CYPRINADA. 
A group of fine shells, many of which are of 
large size, is thus named after the principal genus, 
Cyprina of Lamarck; though the appellation of 
the genus and that of the family are alike objec- 
tionable, as they have long been pre-occupied with 
the slightest possible terminal difference by the 
family and genus of the Carps among Fishes. 
The Mollusks of this group are distinguished by 
thick solid shells, often clothed with an epidermis, 
but usually smooth on the surface, or if sculptured, 
only with concentric lines running parallel to the 
edges of the valves. They vary in colouring, 
some being brilliant, others sombre. The hinge 
has strongly developed teeth, and an external 
ligament. The pallial impression is scarcely 
sinuated in its course. ‘‘ This depends on a pecu- 
har feature in the organization of the animal, 
which has, instead of distinct and produced siphonal 
tubes, only rudimentary ones in the shape of two 
scarcely separated orifices.” The foot is thick and 
tongue-like. 
GENUS JSOCARDIA. 
This genus presents many points of affinity with 
the Cockles, and some with the great Clamps 
(Chama) of tropical seas. The shells are large, 
very convex, almost globose, heart-shaped, with 
the beaks much inrolled, curving forwards and 
outwards; the hinge is composed of two flattened 
teeth. The animal will be described presently. 
The form of the valves has given the name of 
Heart-shell to the only British species, /socardia 
if 
