LOWER HELDERBERG ROCKS. 
323 
Platyceras perplicatum (n. s.). 
Plate LIX. Fig. 8. 
Shell obliquely subcorneal, arcuate, with the minute apex incurved, 
making scarcely a single volution ; upper part of the volution smooth, 
becoming plicate below, and much extended on the anterior side at the 
aperture : aperture nearly round or longitudinally broad-oval; peri¬ 
stome sinuate. 
Surface marked on all sides by depressed rounded plications, about 
eighteen of which may be counted on the margin of the aperture. Entire 
surface marked by transverse lamellose strife, which are crowded to¬ 
gether in concentric wrinkles. 
Fig. 8. Anterior view of the specimen. 
Geological position and locality. In the middle portion of the group : Schoharie 
county. 
Platyceras plicatile (n. s.). 
Plate LIX. Fig. 10 a , b. 
Body of the shell nearly straight, somewhat depressed - conical : apex 
minute, consisting of about one and a half closely contiguous volutions, 
below which they become free ; the contiguous volutions and the upper 
part of the free volution are smooth, becoming plicate below, the pli¬ 
cations dichotomizing on the middle of the shell : aperture reflexed; 
peristome sinuate. 
Surface marked by transverse lamellose striae. 
This species, in its plicate character, resembles the preceding; but the body of 
the shell is nearly straight, and much more depressed than in P. perplicatum , while 
the apex makes at least one more volution. The single specimen figured is the only 
one that has been obtained during many years of continued collections in the Lower 
Helderberg rocks. 
Fig. 10 a. View of the upper side of the shell. Fig. 10 b. View of the aperture. 
Geological position and locality. In the middle portions of the Lower Helderberg 
group : Albany county. 
