TO GEOLOGY. 65 



been observed, eight being from the Crag. Lamarck does 

 not mention any fossil species. M. Deshayes gives nineteen 

 species in his Tertiary Tables. Mr Say has noticed two 

 species in the Tertiary of Maryland ; Mr Conrad two in 

 that of Claiborne. 



FAMILY CONCEDE. 



GENUS CYTHEREA. Lamarck. 



C. globosa. Plate 2. Fig. 40. 



Description. Shell very much inflated, subrotund, very 

 finely and transversely striate ; swollen over the umbones ; 

 lunule widely and beautifully cordate ; beaks very large, 

 recurved ; teeth elevated and disposed to be conical ; exca- 

 vation of the palleal impression conical ; cavity of the shell 

 very deep and rounded; margin entire. 



Diam. 1.1, Length 1.3, Breadth 1.6, of an inch. 



Observations. This is perhaps the most globose of all 

 the species yet known. It is remarkable for its capacity 

 and its high recurved beaks, in which it has some resem- 

 blance to the genus Isocardia. It is this which gives the 

 impression of the ligament a curve of small radius. The 

 excavation of the palleal impression is more angular than 

 in any species I have noticed. The two central teeth in 

 the right valve are erect and close, with a deep cleft be- 

 tween them. On the edge of the right valve there is a 



