No. 109.] 61 



in the centre ; beak scarcely incurved ; mesial elevation obtuse- 

 ly angular ; hinge-line equal to or a little less than the width 

 of the shell ; area of medium size, well defined, and extending 

 to the extremities of the hinge-line. Surface marked by from 

 twelve to fourteen rounded, little elevated, simple costse on each 

 side of the lobe and mesial sinus ; concentrically marked by 

 imbricating lamellse, which are striated upon their surfaces and 

 granular on the edges. 



In many specimens there are faint indications of a fold on each side of 

 the mesial sinus, and of several upon the corresponding mesial elevation : 

 this character, however, is not constant in the specimens examined. 



Geological position and locality. In the Shaly and Upper Pentamerus 

 limestones of the Lower Helderberg group in Albany and Schoharie coun- 

 ties, Hudson, etc. 



Spirifer concinna. 



Spteifer modesta ( n. s.). 



Pal. N.Y. Vol.iii, pl.25, f.l. 



Shell small, subglobose : ventral valve very gibbous near the 

 middle and towards the beak, having a shallow undefined sinus 

 extending from the beak to the front : dorsal valve depressed- 

 convex, semicircular or subtriangular j extremities rounded, 

 sometimes an undefined elevation down the middle ; beak 

 scarcely extending above the hinge-line, not incurved ; hinge- 

 line very short and rounded at the extremities ; area triangular, 

 faintly defined, less than the width of the shell, arcuate ; foramen 



