No. 109.] 149 



Chonetes deflecta ( n. s.). 



Shell subliemisplierical ; hinge rather less than the greatest 

 breadth, obtusely angular, or a little contracted at the extremi- 

 ties : dorsal valve concave ; area linear, and having in the mid- 

 dle a small projecting process : ventral valve convex, gibbous 

 over the central and umbonal regions, depressed at the extre- 

 mities; area of medium breadth, arcuate, and extending ob- 

 liquely upwards; foramennarrow, triangular, partly or entirely 

 closed by its pseudo-deltidium and the dental process of the 

 other valve ; cardinal margin garnished by four or five tubular 

 spines. Surface ornamented by distinct and prominent radial 

 striae which number about fifteen to twenty near the beak, but 

 which increase by intercalation and bifurcation to about thirty 

 to thirty-two at the border : extremely fine closely arranged 

 concentric strise may be seen by the aid of a good lens. Surface 

 near the lateral extremities smooth or with slight radiating 

 undulations, Avith more distinct concentric strife, which are 

 likewise often more conspicuous on the concave than on the 

 convex valve. 



Resembles C. gibbosa, but is not so convex on the umbo of the ventral 

 valve, and is less strongly arched : it is also less extended on the hinge, 

 and has fewer and more elevated striae. The bifurcation and implantation 

 of striae usually take place upon the upper half of the shell, and the striae 

 are often quite simple below the first third of the shell. The hinge extre- 

 mities are not unfrequently bent downward or toward the umbo of the 

 ventral valve. 



This species, in its general aspect, resembles the young shells of Tro- 

 pidolepius carinatus ; but the striae are more numerous. 



Geological position and locality. In the shales of the Hamilton group : 

 Canandaigua lake shore. 



Chonetes pusilla (n. s.). 



Shell small, nearly semicircular ; hinge about equalling the 

 greatest breadth, rather obtusely angular at the extremities : 

 dorsal valve concave ; area unknown : ventral valve gibbous 



