58 



Senate 



extended. Surface marked by from four to six strong and ab- 

 ruptly elevated plications on each side of the mesial sinus and 

 elevation, concentrically marked by strong imbricating lamellae, 

 which are abruptly arched in passing over the plications, giving 

 an extreme roughness to the surface. In well preserved speci- 

 mens, finer longitudinal lines mark the surface of these lamellse : 

 in ordinary specimens, the concentric lamellae are more closely 

 arranged and more distinctly imbricate towards the margin ; 

 while near the beaks they are more distant, and are scarcely 

 imbricate. 



Geological position and locality. Lower Helderberg limestone, Albany 

 county. 



'*™™**^*^ 2 



Spieifer peelamellosa. 



Spirifer cycloptera ( n. s.). 



Pal. N.Y. Vol. iii, pi. 25, f. 1. 



Shell semicircular; extremities of the hinge-line more or less 

 symmetrically rounded : ventral valve gibbous; beak mode- 

 rately elevated, more or less incurved ; sinus moderately deep, 

 curved on the sides, and nearly flat in the middle : dorsal valve 

 very convex towards the middle, the mesial fold abruptly 

 elevated and very prominent j beak little elevated above the 

 hinge-line, and scarcely incurved ; area moderate, scarcely 

 extending to the extremity of the hinge-line ; foramen large. 

 Shell marked by five to seven rounded plications on each side 

 of the mesial line, concentrically marked by fine close imbri- 



