CLINTON, LOWER UELDERBERG, CHEMUNG, AND WAVERLT GROUre. 455 



size, rounded; width at the base equal to three-fourths of the length of the ante- 

 lioi- side; Icnf^th of the posterior side one-half that of the anterior; ri<^ht and 

 left side usually equally developed, but on one speci- 

 men the right side has a little the greater develop- 

 ment. On the anterior side there is a conspicuous 

 rounded or subangular elevation extending from the 

 apex to the base ; on the posterior 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 shal- 

 low depression, of the same extent as the elevation. 



Apeiture circular; peristome slightl}' 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 disj^osed ; the radii are crossed by fine 

 concentric strife ; the surface presenting a cancellated ai)pearance when the specimen 

 is well preserved. 



One specimen measures as follows : Length of the anterior side 32 mm., of pos- 

 terior 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 Plati/ceras hreve of the same locality, 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 stritc, the surface of P. hreve 

 being marked by elongate pustules ; from Platijceras striatum it may be distinguished 

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

 it is without the conspicuous ])lication8 characteristic of that species. It resembles 

 Platycfras mitelliforme in having a prominent carina, but it is a larger form and the 

 apex is not bent or incurved. From Platyceras conicum it may be distinguished by 

 the absence of conspicuous plications ; and from P. carinatum by the straight apex 

 and the absence of conspicuous plications. 



Formation and localitij. Chemung group, three miles north-west of Warren, 

 Warren county, Pennsylvania. 



