CORNJFEROUS LIMESTONE. 
171 
The following illustrations present some of the most common forms of this rock in western 
New-York, though there are many others which perhaps are equally abundant. 
1. Atrpya scitula. 
2. Paracyclas elliptica. 
3. Strophomena acutiradiata. 
4. Strophomena crenistria. 
5. Delthyris duodenaria. 
6. Pleurorhyncus trigonalis. 
C a. Pleurorhyncus trigonalis. 
1. Atrypa scitula, n. s. — Obovate, compressed towards the base ; lower valve very convex, 
with a produced incurved beak ; upper valve convex in the middle, with a small, rather pro¬ 
minent beak. The shell is very glabrous, with faintly perceptible concentric lines ; it may 
be distinguished from any other in the rock, by the extension of the beak of the lower valve. 
Locality —Williamsville, Erie county. 
2. Paracyclas elliptica, n. s. — Shell broad oval; beaks scarcely prominent ; surface 
marked by concentric lines; valves equally convex; very much elevated on the umbones. 
Shell the size of the figure, and larger ; it is readily distinguished by the figure alone-. 
I am indebted to Dr. Everitt, of Batavia, for specimens of this fossil. 
Generic name from its similarity to the Cyclas. 
Locality —Le Roy, Genesee county. 
3. Strophomena acutiradiata, n. s. — Lower valve convex, slightly impressed in front and 
on each side ; hinge line extended beyond the width of the shell, and obtusely angulated at 
the extremities ; surface covered with sharp striae, which bifurcate toward the margin. 
Locality —Five miles east of Buffalo. Very abundant in the higher strata of the rock. 
4. Strophomena crenistria, n. s. — Semi-oval; lower valve slightly convex; upper one 
nearly flat; surface covered with line diverging striae, the spaces between which are crossed 
by concentric lines ; upon the striae, these lines produce elevated points or crenulations; hinge 
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