LOWER HELDERBERG ROCKS. 
a a r 
below, marked on the lower side by a sharply defined spiral groove, 
and on the upper side by a broader depression having a narrow rounded 
dorsal lobe and a subangular ridge above ; while below, or within the 
narrow groove on the lower side, is a less strongly defined parallel 
ridge : aperture subquadrangular; peristome sinuate. 
Surface marked by transverse undulating ridges, and by fine longitudinal 
abruptly undulating striae, which, under a lens, appear to be crenulate. 
This small specimen appears to be a mature shell, and possesses characteristics 
not observed in any other species. It bears a remote resemblance to P. trilobatum; 
but the volutions are fewer, that one having more than two contiguous volutions, 
and, when of the size of the specimen here figured, having a very different form. 
Fig. 1 a. View of the upper side of the spire. 
Fig. 1 b. The lower side, showing the narrow groove in the last volution, 
Geological position and locality. In the upper part of the shaly limestone of the 
Lower ITelderberg group : Becraft’s mountain, Columbia county. 
The following species are from the Upper Pentamerus limestone, and 
have not been observed in the Shaly limestone below. 
Flatyceras clavatum (n. s ). 
Plate LXY. Fig. 2. 
Shell spiral; the apex consisting of about two symmetrical contiguous 
volutions, which are gradually expanding : below the second volution 
the shell is expanded somewhat abruptly, swelling out in an ovoid 
form : aperture elongate-ovate; peristome sinuous. 
Surface marked by fine undulating lamellose transverse striae, which, in 
well-preserved specimens, are crossed by longitudinal undulating striae. 
This species, in the extreme length of the aperture and form of the body-volution, 
differs from any other in this formation. 
Fig. 2. A specimen of this species, from which the shell is nearly exfoliated. 
Geological position and locality. In the upper pentamerus limestone : Schoharie 
county. 
[ Paleontology III.] 
43 
