CONCHOLOGY. 57 



V. imhricata. The imbricated Venericardia. PL 9, fig. 1 . 



Species almost round, having convex longitudinal ribs, cov- 

 ered with imbricated rough scales ; inferior margin rounded 

 and dentated ; more and more equilateral ; the two teeth 

 short and oblique. 



FAMILY X. 



Cardiacea. Five genera. 

 1. Cardium. Cockle, or Heart Shell. Forty-eight species. 



This genus received its name from its resemblance to a 

 heart {Kapdia). It is so well defined by Linnaeus that no al- 

 teration was made by Lamarck, except in making two di- 

 visions of them ; the first distinguished by having the ante- 

 rior side as large or larger than the posterior, and no distinct 

 angle at the apex ; the second by possessing carinated or an- 

 gular umbones, and the posterior side often much larger than 

 the anterior. These shells are found at a small depth in the 

 sand on almost every seashore. 



Shell inflated, equivalve, sub-cordiform (when seen an- 

 teriorly), generally costated from the summit to the circum- 

 ference ; summits very evident ; slightly recurved forward ; 

 hinge complex, similar, formed by two oblique cardinal teeth, 

 articulating with the corresponding teeth on the other valve ; 

 two distant lateral teeth on each valve ; ligament dorsal, pos- 

 terior, and very short. 



H 



