OE DENISON UNIVERSITY. 
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the peristome, is rather concave, the transverse strias are more regular 
and often more conspicuous than the revolving, otherwise the agree- 
ment is close. With B. galericulatus, 4 feet below congl. I. 
Genus Platyceras. 
Of this genus six species are reported by Prof. Winchell from 
Ohio, viz: P. bivolve, P. haliotoides, P. hertzeri, P. paralium, P. ro- 
merium, and P. subplicatum. 
Platyceras hertzeri, Win. 
(Plate II, Fig. 24, and Plate V, hh’g. 8.) 
The difficulty of distinguishing the variable species of Platyceras 
rather increases than diminishes whh the accumulation of specimens. 
The present species, which may be recognized by its moderately large 
size and irregularly plicate, nodulose surface, and compressed form 
extends from the free-stone into conglomerate II. There is generally 
a poorly defined carina near the outer margin as well as irregular trans- 
verse plications. From P. haliotoides it is distinguished by the less 
closely coiled spire. 
Platyceras haliotoides, w. and w. 
(Plate II, Fig. 23.) 
Our figure illustrates a small and not particularly characteristic 
specimen. Many specimens agree fully with the Illinois types, while 
others pass toward P. hertzeri. The upper surface is convex, with 
only a very faint revolving groove or none, the outer surface being 
narrowly rounded, the aperture very oblique. From P. hertzeri it may 
also be distinguished by the closely incoiled spire. With the last. 
