96 AMERICAN JOURNAL 



DESCRIPTIONS OP NEW FOSSIL MOLLUSCA, PRINCI- 

 PALLY CRETACEOUS. 



BY T. A. CONRAD. 



PACHYOAEDIUM, Conrad. 



Elevated, thick, cardinal plate broad ; ligament deep and ob- 

 lique ; anterior cardinal tooth in the left valve slightly oblique 

 or nearly direct, prominent, compressed, triangular ; anterior 

 lateral teeth distant, very prominent, with a pit on the inner 

 side ; sculpture, radiating little prominent ribs on the posterior 

 side. 



P. SPILLMANI, Conrad. 



This genus is as easily recognised as Protocardia^ but, unlike 

 the latter, it contains only two species, both of which existed in 

 the Chalk period, one in Mississippi and the other in India. The 

 Indian species, Q. bisectuni, Forbes, has more nuinerous ribs, 

 which cover half the surface ; but the American shell has few^er 

 ribs, which do not extend so far as the middle of the valves. The 

 former has much more elevated beaks than the latter. 



This genus has not been found in any formation later than the 

 Oligocene, and yet one recent shell, P. Belelieri, Adams, lives 

 in the Soloo seas, in deep water, 



CARDIUM, Liun. 



C. RiPLEYANUM, Conrad. — PI. 9, fig. 6. 



Description. — Suborbicular, equilateral, ventricose ; ribs 21, 

 broad anteriorly, nai-row posteriorly, interstices crossed by pro- 

 minent minute lines. 



Locality. — Haddonfield, N. J. 



GEMMA? Deshayes. 

 G. CRETACEA, Conrad. — PI. 9, fig. 19. 



Description. — Triangular, subequilateral, convex, smooth and 



