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. 



PLATE III, FIGS. 8-10. 

 Platyceras aurii-iilnt urn Hall. Illustrations of Devonian Fossits: Gasteropoda, pi. 3, figs. 8-10. 1876. 



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 carinae 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 carinaa, 

 while the remaining portion of the surface is traversed by smaller and less 

 distinct elevations, of which five occupy the dorsum towards the aperture. 



