4 PALAEONTOLOGY- OF NEW YORE. 
Surface marked by concentric undulating strife, which become sublamellose 
towards the aperture, and are sometimes closely crowded and wrinkled 
with numerous knots or nodes. Peristome deeply sinuous; the width 
from the anterior to the posterior side a little greater than the transverse 
diameter. The length of the shell is one inch and a half or more, with 
the aperture a little less. 
This species approaches the P. pyramidatum of the Lower Helderberg group, 
but is less elongate, the peristome is more sinuous, and the indication of longi¬ 
tudinal ridges and depressions is more distinct; the crowded, wrinkled and 
nodose striae are likewise a distinctive feature. 
Formations and localities. In the Hamilton group, Ontario county; and in the 
Upper Helderberg limestone, at Darien and Williamsville, *N. Y. 
Platyceras (Orthonychia) perplexum. 
PLATE XI, FIGS. 1-3. 
Platyceras perplexum Hall. Illustrations of Devonian Fossils: Gasteropoda, pi. 2. 1876. 
Shell obliquely conical, apex minute, closely incurved, or making a part of one 
volution. The body-volution slightly curved, expanding gradually from 
above to the middle of the shell, below which it spreads more rapidly 
upon one side, becoming strongly plicated; the plications beginning 
above the middle of the shell, and sometimes at a short distance below 
the apex, and increasing in number and strength towards the base. 
Aperture subovate ; peristome deeply sinuate. 
Surface marked by close concentric strife of growth which become lamellose, 
and crowded into undulating bands crossing the radiating ridges. 
This is an extremely rare form, and is quite distinct from any of the other 
species; although presenting in the form of the body-volution an approach to 
some varieties of P. Thetis, it has not the same degree of arcuation, and has 
never the distinctly convoluted nucleus. 
This species bears some resemblance to P. perplicatum of the Lower Helder¬ 
berg group; but a comparison of specimens shows them to be quite distinct. 
Formation and locality. In limestone of the Upper Helderberg group, in 
Onondaga county, N. Y. Communicated by Prof. E. A. Strong. 
