112 



[ Senate 



in the middle, sloping toAvards the front and lateral margins, 

 depressed or concave near the umbo : ventral valve deeply 

 concave, except at the beak ; foramen narrow, closed ; area 

 wide, vertically striate. Siirfoce marked by strong,- somewhat 

 unequal radiating strise, which bifurcate three oi- four times 

 between the umbo and the margin. 



This shell is allied to S. woolworthana of the Lower Heldcrberg shaly 

 limestone, but differs ia being more strongly resupinate, and in the cha- 

 racter of its striae ; those of S. vioolviorihana being more irregular, and 

 increasing generally by abrupt implantation, while those of the present 

 species usually bifurcate very regularly ; in consequence of which, those 

 at the margin are smaller than those near the umbo. It is also nearly re- 

 lated to a species in the Schoharie grit, S. 1 



Geological position and locality. Limestone of the Upper Helderberg 

 group, Albany and Schoharie counties ; and along the outcrop of the same 

 formation as far as Erie county, N.Y, 

 1 



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SxROPnOMENA A3IPLA. 



