456 DESCRIPTIONS OF NEW SPECIES OF FOSSILS FROM THE 



PLATYCERAS IN.EQUALE Simpson, n. sp., Fig. 25. 



Shell small, subangularlj ovate ; apex minute, incurved, making less than one 

 turn, very thin and angular; inclined or twisted to the right. The body of the shell 



expands rapidly ; anterior side curved, sometimes 

 forming nearly half a circle ; posterior side also 

 curved, but in a lesser degree; width of base from 

 one-half to three-fourths the length of the anterior 

 side ; posterior side one-third the length of the 

 anterior. 



The left side is flattened or only very slightly convex, and is often nearly or 

 quite at right angles to the base, making a sharp angle or ridge between the side and 

 the back of the shell. The right side is convex and much more developed than the 

 left. In front the shell becomes flattened near the margin. On the left side, about 

 half way between the base and angular carina, there is a low rounded ridge, com- 

 mencing near the apex and continuing the length of the shell, though this feature in 

 many of the specimens is obscure. 



Aperture circular or broadly oval. 



Most of the specimens observed are casts or macerated so that the surface char- 

 acters are obsolete. On some of the specimens there are evidences of strong radiating 

 striiE or elongate pustules, and when well preserved there are numerous concentric 

 stria\ 



The characteristics of this species are the pinched appearance of the apical 

 portion, and its inclination to the right, and the much greater development of the 

 right side; in the latter feature it resembles Platyceras cymbeum, but it is a much 

 smaller shell, and the plications are very much less prominent ; from Platyceras mitel- 

 llforme it may be distinguished by the inequality of its sides, in that species the 

 prominent ridge being in the middle of the shell, both sides being equally developed. 

 Formation and locality. Chemung group, four miles north-west of Warren, 

 Warren county, Pennsylvania. 



PLATYCERAS MITELLIFORME Simpson, n. sp., Fig. 26. 



Shell small, obliquely arcuate from the base ; apex incurved, making part of one 

 volution; below which the body volution rapidl}^ increases in size. Width at the 

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

 less than one-half of the anterior ; right and left sides equally developed. 



Anterior side convex, with a prominent, broad, rounded carina along the middle; 



