342 PALEONTOLOGY OF NEW YORK. 



Formation and locality. In the shales of the Hamilton group, near Norwich, 

 Chenango county, N. Y. 



PaL^ONEILO BREVIS. 



1"LATK L, FIG*. 24-33. 



PaltBorurilo brevis. Hall. Pi-elim. Notice Laiucllibi-aiirhiata, 2, ji. 10. 1S70. 



" " " Pal. N. Y., vol. V, pt. 1. Plates ami Explanations : PI. 50, figs. 24-33. 1883. 



Shell small, ovate, or ovate-sub-triangular; length about ono-thii-d greater than 

 the height ; basal margin gently curving, with a slight constriction toward 

 the posterior extremity. Cardinal line arcuate. Anterior end usually short 

 and regularly rounded. 



Valves convex below, gibbous in the middle and on the umbonal ridge. 



Beaks usually at about the anterior third or a little posterior thereto, 

 prominent, moderately elevated above the hinge-line. Umbonal slope 

 marked by a slight flattening of the shell, which produces a gentle constric- 

 tion in the post-inferior margin. This depression is rarely margined on each 

 side by an undefined elevation. 



Surface marked by fine, even, concentric striae ; the casts exhibiting only 

 the stronger elevations which give an irregular appearance to the concentric 

 striae. Anterior nmscular impression very strongly marked. Posterior scar 

 large and shallow. Hinge marked by numerous minute crenulations. 



Three specimens of this species measure respectively 21, 20 and 14 mm. 

 in length, and 14, 12 and IC inm. in height. 



This species is allied to P. constrida, but is more gibbous, less curved along 

 the basal margin, and the constriction of the posterior end is so slight as to be 

 scarcely detected in most individuals. 



Formation and localities. In some shaly calcareous sandstones of the Chemung 

 group, at Franklin, Delaware county ; in arenaceous shales, at Philipsl)urgh, 

 Alleghany county, N. Y., and at Lawrenceville, Tioga county. Pa. 



