by concentric elevated lines, which do not penetrate into 

 the interstitial narrow spaces, and which are obsolete on 

 the umbo, and on the anterior side : inner margin deeply 

 crenate : hinge with two diverging teeth, separated by a 

 large cavity on the right valve ; and on the other, a single 

 large triangular, prominent, recurved tooth, closing into 

 the cavity. 



SYNONYM. 



Venericardia tridentata, Nob. Joum. Jicad. Nat. 

 Sc. Vol. 5, p. 216. 



OBSERVATIONS. 



This interesting shell was discovered by Mr. Stephen 

 Elliott, on the coast of South Carolina. 1 formerly placed 

 it, with much doubt however, in the genus Venericardia, 

 but I think it corresponds better with Cardita as now esti- 

 mated, inasmuch as the teeth are not all oblique. 



The large recipient cavity of the hinge of the right valve 

 is somewhat similar, though wider in proportion, to that 

 of the corresponding valve of Cypricardia modiolaris, a 

 very entire specimen of which was sent to me by Mr. 

 Hoeninghaus. 



REFERENCE TO THE PLATE. 



Figs. 1, and 2, Exterior and interior enlarged views of tlie right valve. 



" 3, Outline to shew the natural size. 



" 4, Enlarged hinge of the left valve. 



" 5, Enlarged profile view of the teeth of the right valve. 

 PI. 40. 



