86 PALAEONTOLOGY OF NEW YORK. 



Pleorotomaria quadrilix, n. sp. 



PLATE XXX, FI(i. 18. 



Shell trochiform, depressed-conical, a little higher than wide. Volutions five 

 or six, moderately convex on the upper side, the higher ones minute, or 

 gradually increasing in size from the apex and becoming somewhat ventri- 

 cose. Aperture unknown. 



Surface marked by simple sharp equal concentric striae, which make a slight 

 curve just below the suture, and are thence directed backward to the 

 upper margin of the peripheral band. The striae are about equal to half 

 the space between them ; below the peripheral band on the outer volution 

 they are nearly vertical for a short distance. The band is compound, 

 being limited above and below by a canaliculate belt, which includes a 

 somewhat wider depression between. There are no visible revolving 

 striae. 



This species differs conspicuously from any of those described in this volume 

 by the character of the peripheral band, which presents the appearance of 

 being limited above and below by a sharply grooved carina leaving a narrow 

 intermediate space. The absence of revolving carinae, other than those of the 

 periphery, is also a distinguishing feature. In the strength of the concentric 

 striae it is intermediate in character between the P. nitella and P. adjutor. In the 

 character of surface striae and the peripheral band it is similar to P. costulato- 

 canaliculata of Sandberger; the volutions are about equally convex, but the 

 spire is more elevated, and the band appears entirely above the suture-line in 

 the higher volutions. In all its essential features, except in the greater eleva- 

 tion of the spire, this species corresponds to the P. lenticularis of Goldfuss, from 

 the Devonian rocks of Nassau. 



This fossil is extremely rare in the rocks of New York, since, at the 

 present time, we know but a single example. 



Formation and locality. In the Upper Helderberg limestone at Babcock's 

 Hill, town of Bridgewater, Oneida county, N. Y. 



