1889.] NATURAL SCIENCES OF PHILADELPHIA. 293 



oblongata. Though some recent writers have greatly extended the 

 limits of the genus and embraced a variety of other shells, it would 

 seem that this enlargement of the generic group is of very question- 

 able utility. It is very possible that this is the same form as that 

 di scribed by Hall as Platyeeras cupulas, in which case the latter 

 term takes precedence. 



II. Species from the Kixderhook Beds. 

 Naticopsis depressa Winchell. 



Naticopsis depressa Winchell, 1863. Proc. Acad. Nat. Sci. Phila., 

 p. 22. 



No authentic examples from the lower beds of the Burlington 

 section have come under notice, though the collections include 

 several casts which may belong here. If this inference is correct 

 the species certainly presents characters which differ very essentially 

 from the typical forms of the genus. 



As originally established by McCoy, in 1844, Naticopsis embraced 

 certain paleozoic shells, the best American exemplification of which, 

 perhaps, is the form described by Norwood and Pratten as Natlca 

 ventrieosa from the Coal Measures. The most characteristic shells 

 of the genus are therefore comparatively thin, with the spire very 

 small and short ; the outer labrum thin, as is also the callosity of the 

 inner lip ; the last whorl usually more or less noticeably flattened or 

 slightly concave on the upper half and ornamented towards the 

 suture by numerous, small, short, equidistant cost* parallel to the 

 lines of growth; surface otherwise smooth. A number of species 

 have been erroneously referred to the genus, while some others 

 described under different generic titles must evidently be transferred 

 to this group. There are, perhaps, a dozen valid species of Naticopsis 

 now known from the American paleozoic rocks. 



Platystoma bivolve (White anil Whitfield). 



Platyeeras bivolve White and Whitfield, 1862. Pi-oc. Boston Soc. 

 Xat. Hist., vol. VIII, p. 302. 



The recognition of this genus in the lowest division of the Carbonic 

 is of considerable interest, as this is the second American species 

 recorded above the Devonian. A recent examination of the type 

 specimens reveals a very noticeable departure of this form from 

 Platyeeras, and particularly from the immature shells of Platyeeras 

 ventricosmn Conrad, with which it has been compared. The spire in 

 P. bivolve is much more elevated than in the other specie.-, while 



