3«4 PALEONTOLOGY OF NEW-YORK. 



Surface marked by fine undulating transverse striae, which are crossed 

 by much finer obscure or obsolete longitudinal striae. 



This species differs from the preceding, in spreading less rapidly from the apex, 

 and in being more gibbons on the back of the last volution, while it does not show 

 the fine plications on the right side of the shell near the aperture. 



The specimen figure 6 a 6 has been referred with doubt to this species, but is 

 probably distinct; and fig. 6 c, though having some of the featores of this species, 

 has been vertically compressed, which renders it more rotund : it probably belongs 

 to the preceding. 



Fig 6 rf. View of the aperture of a large specimen of this species. 



Fig. 6 e. A similar specimen, with less strongly plicated margins and a smaller spire. 



Fig. 6 f. The upper side of the spiro of fig. 6 e. The specimen is not quite symmetrical in 

 its convexity. 



Fig. 6 g. The upper side of the spire of the specimen fig. 6 d. 



Fig. 7 a. The lower side of a smaller specimen, showing strong plications. 



Geological position and locality. In the central portion of the Lower Hcldcrberg 

 group : Albany county. 



Platjceras sulcoplicatum ( n. s). 



Plate LIX. Fig. 7 b. 



Shell irregularly subhemispheric : apex posterior, minute, consisting of 

 a single plain volution ; body volution abruptly expanding, ventricose : 

 aperture somewhat quadrangular; peristome sinuate. 



Surface very strongly plicate ; plications four or five, sulcate, with one 

 or two shallow grooves-. 



This species is very peculiar in its broadly expanded last volution, which is more 

 strongly plicated than any other species of the same size in this group of strata. 

 The figure does not well represent the specimen. 



Fig. 7 6. The figure represents the specimen lying with the aperture downward. 



Geological position and locality. In the central part of the shaly limestone of the 

 Lower Helderberg group : Schoharie county. 



