OE DEXISON UNIVERSITY. 



91 



the peristome, is rather concave, the transverse striae 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 11, Fig. 24, and Plate V, Fig. 8.) 



The difficulty of distinguishing the variable species of Platyceras 

 rather increases than diminishes with 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. 'I'here 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, ^^- and w. 



(Plate II, Fig. 23.) 



Our figure illustrates a small and not jiarticularly 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. 



