46 FIFTEENTH REPORT ON THE CABINET OF NAT. HISTORY. 



I 



PLEUROTOMARIA SULCOMARGINATA (Conrad). rjA'IO 



Pleurotomaria sulcomarginata : Conrad, Jour. Acad. Nat. Sciences, Philadelphia, 



Vol.viii, pa. 272, pi. 16, f. 13. 



" Trochiform : outer margin of the large volution bicarinated, with 

 " an intermediate sulcus; volutions with two distant spiral lines, 

 " and crossed by oblique striae." 



This is the most common species of Pleurotomaria in the Hamilton 

 group, occurring in all places east of Seneca lake, and often abundant in 

 the coarser shales of Madison county. To the west of Seneca lake it is very 

 restricted in its vertical range, and is comparatively rare. The form is 

 usually depressed-trochiform, though sometimes seven-eighths of an inch 

 high, with a diameter of one inch. The retral bending of the sharp concentric 

 striae, the distinct carina just above the suture in the upper volutions, and the 

 spiral band on the angular periphery, are distinguishing features. The casts 

 are, however, often rounded on the periphery ; and some specimens in this 

 condition from Maryland measure one inch and a half in diameter and one 

 inch and three-eighths in height, and consist of about five volutions. 



PLEUROTOMARIA ROTALIA ( n. s.). T/. d 

 Shell small, depressed-trochiform. Spire consisting of about four 

 volutions. Apex minute, the volutions gradually expanding to 

 the aperture : slope of the spire from the apex to the periphery 

 nearly in the same plane, being very slightly convex. Aperture 

 subquadrate. 

 Surface very finely and closely striate : strise not prominent; peri- 

 phery marked by a narrow band ; suture - line depressed and 

 narrowly canaliculate. 



This species has nearly the form of P. sulcomarginata; but the band on 

 the periphery is scarcely depressed, there is no carination above the suture- 

 line, and there are no sharp elevated striae. The largest specimens seen are 

 half an inch in diameter and three-eighths of an inch in height. 



Geological formation and locality. In the compact shale or calcareous 

 rock of the Hamilton group, at Pratt's falls, Madison county, N.Y. 



PLEUROTOMARIA EUOMPHALOIDES ( n. s.). ^ | ' i^ 

 Shell depressed - orbicular. Volutions three or four, rising little 

 above the plane of the outer volution, and increasing very gra- 

 dually to the aperture, which is transversely broad elliptical. 



[ August^ 



