667 Platyc. 



the shell regularly increasing in size, rounded ; width at the 

 base equal to three-fourths of the length of the anterior side ; 

 length of the posterior side one-half that of the anterior ; right 

 and left side usually equally developed, but on one specimen 

 the right side has a little the greater development. On the 

 anterior side there is a conspicuous rounded or subangular 

 elevation extending from the apex to the base ; on the poste- 

 rior side is an elevation beginning at about one-half the length 

 of the side from the apex, and continuing to the margin ; on 

 each side of this elevation a comparatively broad shallow de- 

 pression, of the same extent as the elevation. Aperture circu- 

 lar; peristome slightly sinuous at the elevations. Surface 

 marked by fine radiating lines ; at the base there are three in 

 the space of 1 mm., above they are much more closely dis- 

 posed ; the radii are crossed by fine concentric striae ; the sur- 

 face presenting a cancellated appearance when the specimen 

 is well preserved. One specimen measures as follows : Length 

 of the anterior side 32 mm., of posterior 18 mm., height of 

 shell 18 mm. Another specimen, which probably belongs to 

 the same species, is flattened, but that may be due to pressure; 

 it measures as follows : Length of the anterior side 45 mm., 

 of the posterior 22 mm., width at the base 35 mm.; height of 

 shell 18 mm. This species most closely resembles Platyceras 

 breve of the same localiky, but the anterior side is much longer 

 and the posterior side proportionally shorter, the shell more 

 oblique and not so regularly conical ; it has an elevation and 

 two depressions on the posterior side, and the surface has fine 

 radiating strias, the surface of P. hreve being marked by elon- 

 gate pustules ; from Platyceras striatumit may be distinguished 

 as follows : It is more oblique, the posterior and anterior sides 

 are more unequal, and it is without the conspicuous plications 

 characteristic of that species. It resembles Platyceras mitel- 

 liforme in having a prominent carina, but is a larger form and 

 the apex is not bent or incurved. From Platyceras conicum 

 it may be distinguished by the absence of conspicuous plica- 

 tions ; and from P, carinatum by the straight apex and the 

 absence of conspicuous plications— Three miles northwest of 

 Warren, Warren county, Pennsylvania. — Chemung upper heds^ 

 Vlllg. 



