153 [Senate 



In some instances the costae bifurcate, and the central one on the ventral 

 valve more frequently presents this character. Specimens from certain lo- 

 calities show a scarcely perceptible difference in the size of the costae, and 

 no central carination. 



This species is quite peculiar, having no representative as f^ir as at pre- 

 sent known in any of our formations, and may be regarded as the type of 

 a distinct genus. It is likewise very closely allied to those forms which I 

 have designated under the name of Leptoccelia. 



This species has been described by several authors as Leptcsna laticosta, 

 and accredited to Mr. Conrad. This name was originally proposed by the 

 writer, to obviate the confusion arising from the circumstance of two species 

 having been described by Mr. Conrad under the name of S'rophomena 

 carmata : the first in the Annual Geological Report of New- York, 1839; 

 and the second in the Journal of the Academy of Natural Science, in 1842. 

 Among some original drawings and manuscripts recently received from Mr. 

 Conrad, I find the latter designated under the name S. coronata, and the 

 name S. carinata is simply a typographical error as I had always suspected. 

 This species proves to be a Chonetes (C. coronata), and the original Stro- 

 phomena carinata of Mr. Conrad will form the type of the Genus Tro- 



PIDOLEPTUS. 



This species has been recognized in Europe, and is published under the 

 name of Leptcsna laticosta in the Bulletin do la Soc. Geol. de France, 

 Tome iv, pa. 325, pi. 3 ; but it is there represented as having about thirty- 

 two plications, a number much greater than any of our specimens, and it 

 may not unlikely prove a distinct species of the same generic type. 



Geological position and locality. In the Hamilton group in Schoharie 

 county, and at Eighteen-mile creek on Lake Erie; upon the shores of 

 Seneca, Cayuga and Canandaigua lakes, extending in fact throughout the 

 entire breadth of the State from near the Hudson river on the east, to Lake 

 Erie on the west. It likewise occurs in rocks of the same age in Illinois 

 and Iowa. 



1 :---.flSi^b.^._ 2 



TrOPIDOLEPTUS CARINATD8. 



