340 PALEONTOLOGY OF NEW YORK. 



The central portion of the hinge-line is marked by fine crenulations (those 

 of the extreme ant<?rior and posterior are not determined). The post-cardinal 

 margin shows two longitudinal folds above the crenulated hinge. 



Three specimens measure respectively 43, 38 and 34 min. in length, and 

 25, 21 and 20 mm. in height. 



This species, in its general form, bears some resemblance to P. Jecunda and 

 P. mtita, but the umbonal ridge is less defined, the posterior extremity is more 

 extended, and the lamellose striae are more distant. Tlie surface is usually 

 smooth or polished, and the striae scarcely visible to the naked eye. 



The larger proportion of the specimens are from the softer shales, and 

 extremely compressed, while others, in different conditions of preservation, 

 show the anterior half of the shell to be gibbous. The first specimens described 

 were from the soft shales, and gave origin to the name P. perplana. 



Formation and localities. In the shales of the Hamilton group, at Fultonham, 

 and near Summit, Schoharie county ; near Clarksville, Albany county ; on the 

 shores of Seneca and Cayuga lakes ; and in the town of Bristol, Ontario county, 

 N. Y. 



PALiEONEILO ViRGINICA, n. Sp. 

 PLATE XCm, FIG. 14. 



Shell large, robust, elliptical ; length less than twice the height ; basal margin 

 gently curving; posterior extremity doubly truncate. Cardinal line long, 

 gently arcuate. Anterior end large, regularly rounded at the extremity. 



Valves regularly convex in the lower and posterior portions, becoming 

 gibbous in the middle and umbonal regions. 



Beaks at the anterior third, low, little elevated above the hinge-line. 

 Umbonal slope convex, not conspicuously defined in the cast, marked by two 

 low, rounded, diverging ridges, extending to the post-inferior extremity and 

 to the middle of the posterior end, forming a short, linguiform extension. 

 Post-cardinal slope slightly concave. 



Surface marked by fine concentric striae which are fascicuhate, forming 

 undulations on the posterior portion of the shell. The cardinal line, in the 



