LOWER HELDERBERG ROCKS. 305 



8tropliostylus glubosus ( n. s). 



Plate LV. Fig. 8. 



Shell globose. Spire short, obtuse : volutions three or four, rounded ex- 

 teriorly, rapidly increasing in size, the last one symmetrically rounded 

 and very ventricose, the upper margin of the lip extended at its junc- 

 tion with the volution ; aperture subcircular ; suture distinctly cana- 

 liculate. 



ScKFACE marked by extremely fine threadlike undulating stria3, and, in 

 older shells, by faint revolving undulations. 



This species dififers conspicuously from the S. elegans in its more depressed spire 

 and more rotund form, as well as in the canaliculate suture and finer striae. The 

 revolving undulations are too undefined to become a character of importance, unless 

 in better preserved specimens than I possess : they are visible from reflection, on 

 turning the specimen in the light. 



Fig. 8. A cast of the species, preserving a fragment of the shell along the suture. 



Since this plate was engraved, I have obtained specimens of this fossil, with the 

 shell entire, from Becraft's mountain, through the kindness of Mr. Wardle, for- 

 merly of Stockport, Coliunbia county. 



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

 group, and in the compact beds of the same formation : Becraft's mountain and 

 Catskill. 



8ti'opliostyIas obtusus ( n. s.). 



Plate LXVIL Fig. 1 a, b. 



Shell subglobose ; height a little greater than the width. Spire short 

 obtuse, nearly flat above the second volution : volutions about four, 

 very rapidly increasing in size, becoming very ventricose below the 

 second one, and swelling- out laterally ; suture canaliculate, with a 

 distinct ridge just outside the groove, from which the surface slopes 

 abruptly to the general curvature of the volution : aperture round- 

 ovate, contracted behind by the upper edge of the peristome, joining 

 the volution below the middle. 

 [ Paleontology III.] 39 



