LOWER HELDERBERG ROCKS. 307 



ventricose and extending very obliquely from the axis of the shell ; 

 suture canaliculate : aperture round, extremely expanded, the outer 

 lip joining the second volution along its lower side, and extending near- 

 ly to the columella ; columella thickened at its outer margin, and 

 separated by a spiral groove from a parallel fold within. 

 Surface marked by fine closely arranged striae, which, in old shells, 

 become lamellose, particularly towards the margin. 



Fig. 2 a. View of the aperture of a young shell. 



Fig. 2 h. View of the spire of the same, which preserves but two distinct volutions 



Fig. 2 c. View of the spire of a larger specimen. 



Fig. 2 d. A large individual in which the apex of the spire is covered by stony matter. 



Fig. 2 e. View of the aperture of the same. A careful removal of a portion of the stone from 

 the aperture, since this figure was drawn, has shown the columellar margin, the 

 spiral groove within, agd the thickened ridge or callosity beyond. 



Geological position and locality. In the upper pentamerus limestone : Carlisle, 

 Schoharie county. 



Stropliostylus? rotuiidatos (n.s.). 



Plate LVII. Fia. 1 c. 



Shell subglobose or rqtund-ovoid. Spire composed of few volutions, the 

 last one becoming very yentricose and regularly rounded ; aperture 

 nearly circular. 



Surface marked by fine closely arranged lamellose striae, 



The spire, except a little more than the first volution, is broken and worn away, 

 so that its form and entire number of volutions cannot be ascertained. The striae 

 are regular, without appearance of sinuosities; and there remains some evideqce of 

 a columella, though that part of the shell is broken. 



The specimen was originally arranged with the Platyceras billingsi, under the 

 impression that it was a variety of that speciesj but it is evident, on careful com- 

 parison, that it does not belong to that genus. 



Fig. 1 c. View of the spire, with the aperture downwards. 



Geological ■position and locality. In the upper pentamerus limestone : Carlisle, 

 Schoharie county. 



