CARDIUM COCKLE. 161 



Genus. -CARDIUM.* PforaZ, Cardia. 



Generic Character. Shell bivalve, equivalve, 

 nearly equilateral ; shape, convex, the contour of 

 many of the species when viewed with either of 

 the slopes in front, exhibits the form of a heart ; 

 surface either ribbed, striated, or farrowed lon- 

 gitudinally ; margins toothed, the ribs or fur- 

 rows of the two valves being so arranged as to 

 alternate at the margins, and to fit closely into 

 each other ; the hinge has four teeth in each 

 valve, the two central are oblique, approximating, 

 and articulating with the teeth of the other valve, 

 two lateral teeth remote ; the beaks are turned 

 inwards ; the umbones are turgid ; the ligament 

 is external. 



OBSERVATIONS ON THE SHELL AND ITS 

 INHABITANT. 



The Cardium is readily distinguished from 

 the shells of other genera by the peculiarity of 

 its teeth and its cordate form ; its ribs or striae 

 also are invariably longitudinal. The mollusks 

 of this genus are furnished with two short un- 

 equal tubes, fringed with hairs at their ex- 

 tremities ; they have a strong muscular foot 

 which enables them to move with great rapidity. 



* Plate VIII. figures 1, 2. 

 M 



