NAPLES FAUNA IN WESTERN NEW YORK, PART 2 3 I 7 



cap ill aria, a similar type of structure was widespread in the Devonic, 

 and these may have come into the Naples region with the invading fauna. 



Pleurotomaria capillaria Conrad cognata mut (?) nov. 



Plate 19, fig. 27-30 



Shell of medium proportions, with rather rapidly tapering spire and 

 step-form volutions ; attenuate. Whorls five to six, usually overlapping to 

 the slit band. The upper surface of each slopes rather directly outward for 

 more than one half its width and then falls away almost vertically to 

 the suture. The slit band is central, narrow, prominent with sharply 

 defined edges and depressed surface, is continuously exposed to the apex 

 and carries closely crowded, retrally bent concentric striae, which are here 

 more abundant than elsewhere on the surface. 



The surface of the upper division of the whorls carries in early stages- 

 two (second-third whorl) in later growth five (fourth whorl) and in full 

 growth six revolving ridges of unequal size. Of these that nearest the 

 slit band in early growth becomes the most prominent, though eventually 

 one or more ridges may intervene between it and the band. This angulates 

 the whorls, changes the slope and effects the steplike contour. Next to this 

 in size is usually its companion of later introduction, then the other primi- 

 tive ridge nearer the suture is most prominent. On the under side of the 

 body whorl are from 10 to 15 low, flattened, revolving, raised striae of sub- 

 equal size ; in old shells these may become obsolescent. Crossing these 

 revolving ridges of the upper surface are fine, sharp, elevated, concentric 

 lines, 60 to a whorl, directed backward parallel to the aperture and making 

 sharply elevated knots at the points of intersection. On the lower surface 

 these lines are closely crowded together and may become in old stages 

 fasciculate, nearly obliterating the revolving ridges. 



These characters differ from those of P. capillaria in these respects : 



The whorls of the latter are more regularly terraced by the revolving 

 lines, which are fewer and of more nearly equal size ; the prominent knotted 

 line of P. c o g n ata is in the former reduced in strength, and the concen- 

 tric lines are somewhat less in number. 



