294 PROCEEDINGS OF THE ACADEMY OF [1889. 



the inner lip is much thickened, reflexed and anchylosed to the 

 body volution. The form under consideration is with considerable 

 difficulty distinguishable from some individuals of Platystoma 

 niagarense , Hall, notwithstanding the wide separation of the 

 respective horizons of the two species. 



Platystoma as defined by Conrad included those subglobose Natica- 

 like gasteropods, in which the labrnm joined the body whorl at 

 right angles to the axis of the shell. The group is typified by P. 

 ventricosum, but it is very evident that several species have been 

 assigned to the genus, the correct reference ofwhich is very question- 

 able. In an extensive series of a single species, such as may be 

 obtained of P. niagarense at Waldron, Indiana, the shells show an 

 interesting gradation from those precisely like the types to in- 

 dividuals in which the lip is entirely separated from the body 

 whorl, and in some instances the last volution has uncoiled for a 

 considerable distance. These partially evolute forms often approach 

 closely certain Platycerata, and it is very likely that a more careful 

 study of the latter will disclose a nearer relationship betweea the 

 members of the two groups than has heretofore been generally 

 suspected. This tendency of the volutions to uncoil is also very 

 apparent in several Upper Carbonic species of Naticopsis, as well 

 as in various individuals of allied genera. 

 Platyceras cornuforme Winehell. 



Platyceras cornuforme Winehell, 18(53. Proc. Acad. Nat. Sci. 

 Phila., p. 18. 



This is one of the smallest forms of the genus occurring in the 

 lower Carbonic rocks. It has a wide geographic range in the 

 Kinderhook beds, being found not only at Burlington, but also at 

 Lodi and other localities in Ohio. 



P. vomerium Winehell, described from the same horizon has been 

 found only in the form of internal casts in sandstone ; and its 

 specific relations cannot at present be satisfactorily made out, 



Platyceras paralium White and Whitfield. 



Platyceraa jiaralium White and Whitfield, 1802. Proc. Boston 

 Soc. Nat. Hist., vol. VIII, p. 302. 



Examples have been seen from the Kinderhook beds at Le Grand, 

 Marshall county, and Burlington, Iowa; also from Lodi, Ohio. .V 

 careful examination of the type specimens shows that the shell is 

 composed of more than two volutions instead of one, as stated in the 

 original description. The spire, however, is remarkably slender, 



