133 



Fig. 12. 



Cryptonella. 



In casts of the ventral valve, we find the marks of two 

 thin dental lamellse extending to a greater or less distance 

 below the beak. Along the median line in the ventral cast, 

 there is usually a narrow flattened space limited by a slender 

 line ; and on each side a less distinct narrow space, limited 

 in the same manner. In the cast of the dorsal valve, there 

 is a median impressed line, and two of less strength on 

 each side of this. 



The species of this genus, known to me, are the Cryp- 

 tonella {Centronella) julia, and those described as Terebra- 

 tula in the Thirteenth Report on the State Cabinet, and 

 which in the Fourteenth Report were referred to Crypton- 

 ella, viz. Cryptonella (T.) rectirostra, C. (T.) lens, C. (T.) 

 planirostra; and C. eximia, of the Fifteenth Report, as well 

 as a new species from the Schoharie grit. 



The Terebratida lincklceni, which has the external charac- 

 ters of Cryptonella, and which I have referred to that 

 genus, presents some slight differences in the muscular im- 

 pressions, which, taken together with its rotund form, are 

 suggestive of true Terebratula, to which genus it may 

 possibly belong. 



The species of the Genus Centronella heretofore de- 

 scribed, have the ventral valve highly convex or subangular 

 in the middle, with the dorsal valve flattened or concave in 



[Trans. iv.\ 18 



