No. 109.] 57 



SpIRIFER VENTRICOS^i. (n. s.). 



Pal. N.Y. Vol.iii, pi. 14, f.l. 



Shell globose ; valves almost equally convex : ventral valve 

 having a narrow sinus extending down the centre from beak to 

 base; beak projecting above the other, strongly incurved and 

 pointed ( in many specimens the beaks are nearly equal ) : 

 dorsal valve having a central depressed line, but less conspicuous 

 than in the opposite valve ; area very small, concave ; surface 

 marked by concentric lines of growth. 



This species resembles Spirifer pisum of the Niagara group ; but the 

 form is slightly more extended, the beak of the ventral valve more elevated 

 and incurved, and the area more distinct. 



Geological position and locality. Lower Helderberg limestone, Albany 

 county. 



Spirifer ventricosa. 



Spirifer perlamellosa (n.s.). 



Pal. N.Y. Vol.iii, pi. 26, f.l. 



Spirifer rugosa, Hall, in Catalogue. 



Shell trigonal or semicircular, more or less extended on the hinge- 

 line, the extremities varying from obtuse or rounded to extreme- 

 ly mucronate : ventral valve arcuate, the beak much extended 

 beyond the opposite valve, and incurved at the apex ; sinus 

 deep, gradually expanding, and produced in front into a lingui- 

 form extension : dorsal valve convex towards the middle, the 

 mesial elevation very prominent, and the beak closely incurved 

 against the area, or partially closing the foramen of the ventral 

 valve ; area moderately wide, frequently much expanded, and 

 becoming linear towards the extremities where the shell is much 



