GASTEROPODA. 85 



A single individual only has been observed, but the characters are so different 

 from any other in the group that it may readily be distinguished. 



Formation and locality. The specimen is from a loose fragment of calcareous 

 shale, found in the drift at Sexton's, in the town of Catharine, Schuyler 

 county, N. Y., associated with numerous characteristic fossils of the Hamilton 

 group. 



Pleurotomaria nitella, n. sp. 



PLATE XXX, FIG. 19. 



Shell turbinate ; spire suberect, conical, elevated, higher than wide. Volutions 

 six or more, moderately convex above, and obscurely subangular on the 

 periphery, gradually enlarging to the last one which is ventricose ; lower 

 side very convex, and abruptly depressed into the umbilical cavity. 



Surface marked by a revolving carina above and below the peripheral band ; 

 the band is very narrow and prominent, leaving a narrow depressed space 

 above and below it, which gives a carinate aspect to the outer volution. 

 Concentric striae directed backward in a gentle curve from the suture to 

 the upper carina, crossing which they are a little more nearly vertical, 

 and then directed backward to the narrow peripheral band ; below the 

 band they are nearly vertical to the lower carina, where they are directed 

 gently backward. Striae on the lower side a little less distinctly defined 

 than those above. 



This species somewhat resembles the P. adjutor, but is less robust, the 

 spire proportionally higher, the volutions less spreading laterally, the carina 

 above and that below the periphery less prominent, and the upper side of the 

 volution more convex. The concentric striae are much finer, and very 

 different, in their gentle retral curving upon the upper side of the volution, 

 from the straight rigid striae of that species. This fossil is a rare form occur- 

 ling with a species of Loxonema, a Bellerophon and a Coleoprion, which are 

 unknown in any other locality. 



Formation and locality. In decomposing cherty beds of the Upper Helderberg 

 liiiH'stone near Jamesville, Onondaga county, N. Y. 



