340 
PALAEONTOLOGY OF NEW YORK. 
The central portion of the hinge-line is marked by fine crenulations (those 
of the extreme anterior 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 mm. in length, and 
25, 21 and 20 mm. in height. 
This species, in its general form, bears some resemblance to P. jecunda and 
P. muta , but the umbonal ridge is less defined, the posterior extremity is more 
extended, and the lamellose striae are more distant. The 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. 
Pal^oneilo Virginica, n. sp. 
PLATE XCIII, FIG. 11. 
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 fasciculate, forming 
undulations on the posterior portion of the shell. The cardinal line, in the 
