LOWER HELDERBERG ROCKS. 333 



Fig. 11. A fragment preserving a little more than one volution. 



Geological position and locality. In the shaly limestone of the Lower Helderberg 

 group : Becraft's mountain, Columbia county. 



Platyceras iieMlierrji ( n. s.). 



Plate LXIIL Fig. 14 a - e. 



Shell subdiscoidal, with the last volution expanded : volutions about 

 three, nearly in the same plane ; the first two minute and closely in- 

 volved, the last one free, somewhat rapidly expanding, flattened upon 

 the back and becoming ventricose towards the aperture : aperture 

 rounded or broad-oval. 



Surface marked by strong transverse or slightly oblique nodes or ridges 

 upon the dorso-lateral angles of the last volution, about eleven or twelve 

 on each side, which are sometimes connected by a low ridge across 

 the back ( the two upper volutions being rounded and free from such 

 ridges). Entire surface marked by regular even threadlike longitudinal 

 striae. 



This species is very remarkable in its form and surface markings; the volutions 

 being more nearly in the same plane than any other form among all those before 

 me, while the transverse nodes form a very striking feature. The longitudinal strise 

 are very strongly developed, and the transverse striae are not visible on the upper 

 part of the shell. 



In the specimen figured, the shell is preserved near the apex, while the remaining 

 portion is only a cast. Another specimen, which is an older shell, is more rapidly 

 expanded below, and the transverse nodes become obsolescent towards the aperture. 



Fig. 14 a. Dorsal aide of tlie last volution. 



Fig. 14 h. View of the top of the spire. 



Fig. 14 c. The lower side of the shell. 



Fig. 14 d. Posterior view, showing, partially, the aperture. 



Fig. 14 e. Enlargement of the surface, showing the longitudinal striae. 



Geological position and locality. In the shaly limestone of the Lower Helderberg 

 group : Becraft's mountain, Columbia county. 



