64 
PALAEONTOLOGY OF NEW YORK. 
PLEUROTOMARIA, De France. 
Pleurotomaria arata. 
PLATE XVII, FIGS. 1-8. 
Pleurotomaria arata, Hall. Descriptions of New Species of Fossils, etc., p. 14. 1861. 
“ “ “ Fifteenth Rep. N. Y. State Cab. Nat. Hist., p. 42, pi. 5, fig. 13. 1862. 
“ “ “ , Illustrations of Devonian Fossils: Gasteropoda, pi. 17. 1876. 
Shell depressed-suborbicular or obliquely hemispheric. Spire moderately 
elevated; volutions four or more in the entire shell, depressed-convex or 
flattened upon the upper side, and rounded below, gradually enlarging 
from the apex—the outer half of the body-volution being ventricose. 
Aperture somewhat transverse. 
Surface, on the upper side of the volutions, usually marked by strong, regular, 
distinct striae, which often rise in sharp, elevated ridges; occasionally 
finer and more subdued. These striae are parallel to the lines of growth, 
and sometimes appear to have been crenulated by finer revolving striae. 
A well-defined revolving band marks the periphery of the shell, but 
usually (owing to compression of the specimens) this cannot be traced in 
the higher volutions. The lower side of the outer volution is marked by 
fine, equal, revolving striae. 
This species is abundant in the Schoharie grit, in the condition of casts of 
the interior. Individuals retaining the shell are rarely found, but some of the 
stronger markings are not unfrequently preserved on the casts, or as impres¬ 
sions of the exterior upon the enclosing matrix. The diameter of the shell is 
from one inch to two inches and a quarter (smaller specimens are sometimes 
seen); occasional examples of the vertically compressed specimens, attain a 
diameter of two inches and a half; the vertical height in the largest of 
these is about one inch and a quarter. A single rotund form measures one 
inch and tliree-fourths in height, and a little more in its greatest diameter. 
The shell appears to have been distinctly umbilicate. The casts, if not 
distorted, always present a large, circular, umbilical cavity which extends to 
