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 b. 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 c. 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 coluinellar margin, the 
spiral groove within, and the thickened ridge or callosity beyond. 
Geological -position and locality. In the upper pentamerus limestone : Carlisle, 
Schoharie county. 
Strophostylus? rotuirdattis (n. s ). 
Plate LVII. Fig, 1 c. 
Shell subglobose or rotund-ovoid. Spire composed of few volutions, the 
last one becoming very ventricose 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 evidence 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 species; 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. 
