GF CONCHOLOGY. 191 



DESCRIPTION OP A NEW GENUS OP ASTARTIDiE, 



BY T. A. CONRAD. 



CYCLOCARDIA, Conrad. 



Rounded, equivalve, radiately costate, covered with a rough 

 epidermis ; hinge with two robust teeth in the left valve, directed 

 obliquely backward, the posterior one elongated and slightly 

 curved ; anterior tooth of the right valve rudimentary ; pallial 

 impression entire. 



Cardita borealis, Conrad. 



This genus differs from Cardita in being of a less dense 

 structure of the valves, which are often eroded on the ribs, and 

 in having a rough, brown epidermis covering a white unspotted 

 shell. The anterior cardinal tooth is directed obliquely back- 

 ward, unlike that of Oardita, and the anterior muscular im- 

 pression is comparatively longer than in that genus, whilst its 

 northern habitat is very different from that of the Carditce which 

 inhabit the Mediterranean and tropical seas. 



The epidermis, when magnified, shows fine close lines follow- 

 ing the direction of the ribs. 



C. ventricosa, Gould, has a similar form and epidermis, and 

 inhabits Puget Sound, thus agreeing in every essential character 

 with its congener (7. borealis. 



