64 PALEONTOLOGY OF NEW YORK. 



PLEUROTOMARIA, De France. 

 Pleurotomaria arata. 



PLATE XVII, FIGS. 1-8. 



Pleurotomaria arata. Ham,. D oteri pttCM of New Species of Fossils, etc., p. 14. 1861. 



« " " Fifto.Mitli R.-ii. N. Y. State Cab. Nat. Hist., i>. 42, ),1. '), H^'. 13. 1862. 



« '< " Illustrations of Devonian Fossils: Gasteropoda, jil. 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 three-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 



