LOWER HELDERBERG ROCKS. 301 



Platyostouia depressa ( n. s.)- 



Plate LV. Fig. 4 a, 6. 

 Shell depressed-globose. Spire short, little elevated above the body of 

 the shell : volutions three or four, a little depressed at the suture and 

 regularly curving on the top and sides ; aperture round or transversely 

 suboval. Surface somewhat lamellose-striate. 



This species approaches in character to the P. veniricosa, but is much more 

 depressed, and the aperture is often transversely oval. The surface striae, in the 

 partially preserved shell, appear to be more lamellose. 



Fig. 4 a. A lateral view of a small individual. 



Fig. 4 b. The lower side of a similar specimen. The umbilicate character is due to the 

 removal of the columella ; the specimen being a cast, which preserves the 

 impressions of the striaj. 



Since this plate was engraved, I have obtained other specimens from the same 

 rock, which are nearly twice the diameter of those figured; comparing in size with 

 the P. ventricosa figured, but having the depressed-globose form of fig. 4 o, b. 



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

 group : Schoharie, Catskill, and Becraft's mountain. 



Platyustoiiia? subaii(^ulata (n.s.). 



Plate LV. Fig. 3 a, b. 



Shell depressed-subglobose. Spire moderately elevated, consisting of about 

 four volutions, the upper sloping sides of which are somewhat flattened, 

 the last one moderately ventricose and somewhat obtusely angular in 

 the middle ; aperture transverse. Surface unknown. 



This species, in its angular volutions, resembles Pleurotomaria; but since the 

 shell is removed, I have no means of determining satisfactorily its relations. 



Fig. 3 a. A lateral view of the specimen. Fig. 3 b. View of the base of the same. 



The umbilicate character is exaggerated by the removal of the shell, or entirely due to 

 that cause. 



Geological position and locality. In the compact layers of the shaly limestone of 

 the Lower Helderberg group : Albany county. 



