COAL-MEASUEE SPECIES. 345 



outline. I think I can also see some traces of the oblique second angle 

 on the compressed, posterior dorsal region, especially near the beaks, 

 though this is so faintly marked as to have escaped the attention of the 

 artist. 



Locality and position : The original type specimen of this species was found near 

 the base of the lUinois Coal Measures, in "Warren county of that State. I have, how- 

 ever, seen it from the upper part of the Coal Measures in Illinois and western Iowa. 

 The specimen here figured came from the Coal Measures at Greentown, Stark county, 

 Ohio. 



GASTEROPODA. 



Genus PLATYCERAS, Conrad, 1840. 



(Prelim. Report Palieont. N. Y., 205.) 



* Platyceras tortum, Meek. 



Plate 20, figs, lo, b, c. 

 Platyceras tortum, Meek (1871); Proceed. Acad. Nat. Sci., Philad., XXIII., 171. 



Shell very thin, dextral, attaining about a medium size, in young 

 specimens composed of about one and a half to two volutions, subglobose, 

 these first turns being contiguous, rounded, and rapidly increasing in 

 size, after which the next turn, which composes the larger part of the 

 shell, becomes free, very oblique, and increases more gradually in size, 

 thus making the entire outline very obliquely elongate-rhombic; body 

 volution a little flattened on the upper slo2:)e, subangular above, and 

 somewhat prominently rounded near or below the middle ; aperture 

 apparently oval-suborbicular; lip without sinuses. Surface non-plicate, 

 and with only moderately distinct lines of growth. 



Length, 1.36 inches; breadth, about 0.90 inch; breadth and length of 

 aperture, each 0.70 inch. 



I have long been familiar with casts of this shell in the collections of 

 the Illinois Geological Survey, but had some doubts whether they might 

 not be distorted internal casts of a Macrocheilus. The specimens from 

 which the above description was made out, however, retain the thin 

 shell, and show that it is a true Platyceras. Specifically it is more nearly 

 alliedito some of the non-plicated varieties of the New York Upper Silu- 

 rian, P. spirals, than it is to any Carboniferous species known to me, 

 though its first two volutions are more compactly coiled together. 



Locality and position : Greentown, Stark county, Ohio. Coal Measures. 



