170 PROCEEDINGS OF THE ACADEMY OF 



I have concluded to place it provisionally in the genus Plaiyos- 

 toma. 



I should perhaps remark here, that this is certainly not a de- 

 pressed variety of Platyostoma Niagarensis ; and the specimens 

 clearly show tliat they have not been accidentally compressed. In 

 internal casts there is a small umbilical perforation, but this was 

 probabl}' occupied by the columella, before the shell itself was 

 dissolved away. 



Locality and jMsifion. Yellow Springs, Ohio. Niagara group 

 of Upper Silurian. 



PLATYCERAS (ORTHONYCHIA!) LODIENSE, Meek. 



Shell rather small, non-spiral, or merely having the form of 

 rapidly expanding cone, with a backward obliquity that brings 

 the apex nearly over the posterior margin ; lateral slopes nearly 

 straight or slightly concave, and converging to the apex at an 

 angle of about 80°; posterior side vertical and a little concave in 

 outline; anterior slope somewhat more than twice as long as the 

 height of the posterior side, moderately convex in outline, and 

 provided with a ridge or obtuse carina along its entire length; 

 aperture oval suborbicular, being slightly longer than wide; lip a 

 little sinuous anteriorly, immediately on one or both sides of the 

 termination of the central ridge of the anterior slope, which ridge 

 is thus made to terminate in a little projection of the margin. 

 Surface marked by fine lines of growth, most distinct on the an- 

 terior slope, where they curve backward as they approach the 

 mesial ridge, and then abruptlj^ forward in crossing this ridge; 

 extremely faint traces of minute radiating striae apparently also 

 exist. Apex rather abruptly' pointed and directed backward, 

 without any lateral obliquity. 



Length, measuring obliquel}' from apex, 0.91 inch; breadth, 0.82 

 inch; direct length from anterior to posterior margin, 0.96 inch; 

 height of apex, 0.40 inch. 



This species is remarkable for its regular obliquely-conical form 

 and non-spiral apex, which is merely rather obtusely pointed and 

 directed obliquely backward, without the slightest lateral curve. 

 It therefore differs widely in form from the typical species of 

 Platyceras, and agrees more nearly with existing species of Capii- 

 lus. It also resembles a shell figured and described in the third 



[August 15, 



