GASTEROPODA. 
7 
Surface marked by crowded, undulating, concentric striae and longitudinal, 
irregular and undefined folds, which vary greatly in different specimens : 
the latter becoming more distinctly marked as plications near the aperture. 
Peristome sinuous, with numerous indentations corresponding to the folds 
upon the surface. 
In many specimens the surface is marked by abrupt undulations without 
distinct folds or with the folds obscurely developed. Length of shell about one 
inch, with the greatest diameter a little less than half an inch. 
This species is distinguished by the abrupt contraction of the upper part of 
the shell at the beginning of the body-whorl or just below the curvature: while 
the apex, consisting of scarcely more than a single minute volution, is abruptly 
contracted, and proportionally more slender than in most other species. It 
somewhat resembles the P. clavatum of the Lower Helderberg group. 
Formation and localities. In the shales of the Hamilton group on the shores 
of Seneca and Cayuga lakes, Geneseo, Moscow, and other places in Western 
New York. 
Platyceras auriculatum. 
PI.ATE in, FIGS. 8-10. 
Platyceras auriculatum Hall. Illustrations of Devonian Fossils: Gasteropoda, pi. 3, figs. 8-10. 1S76. 
Shell subovoid, extremely arcuate, the nucleus making little more than one 
volution, beyond which the shell at first gradually expands, and finally 
becomes ventricose below, being much more expanded on the right side. 
The back of the shell, to the end of about the second volution, shows the 
existence of a deep dorsal sinus, which at this point becomes filled, and the 
margin of the shell projects, while the peristome has become indented by 
numerous shallow sinuosities, appearing on the surface of the body- 
volution as sharp carinse or subdued plications; each one of which indicates 
the degree of sinuosity in the margin of the shell. The expansion on the 
right side, beginning as described, is marked by three prominent carinae, 
while the remaining portion of the surface is traversed by smaller and less 
distinct elevations, of which five occupy the dorsum towards the aperture. 
