Weller — Kinderhook Faunal Studies. Ill 



in number, gradually expanding, the suture rather strongly 

 impressed ; cross section of each volution subcircular in out- 

 line. The outer volution with a barely perceptible, de- 

 pressed, rounded, revolving ridge a short distance below the 

 suture, marking the position of a moderately deep rounded 

 notch in the peristome. Greatest diameter, 25 mm., height of 

 shell, 18 mm., approximate diameter of umbilicus, 7 mm. 



Remarks. The genus Plaiyschisma is distinguished from 

 Straparollus, where this species has always been placed, by 

 the presence of a notch of greater or less depth in the peri- 

 stome in its outer posterior half. This notch resembles that 

 in the peristome of the Pleurotomaridae, but it does not result 

 in forming a conspicuous revolving band, so that unless the actual 

 margin of the aperture is preserved it is impossible to sepa- 

 rate the species from Straparollus. The genus Platyschisma is 

 represented by several species in the Carboniferous faunas of 

 Europe, but it has heretofore been definitely recognized in 

 America only in the Vermicular sandstone fauna at Northview, 

 Missouri.* In the type specimen of P. barrisi here illus- 

 trated, the peristome is perfectly preserved through a greater 

 part of its length, and the notch is well shown. The summit 

 of the spire is imperfect in the type specimen so that the actual 

 number of volutions in the shell cannot be determined, but 

 another specimen preserves at least four volutions. 



Platyschisma depressa n. sp. 



Pl. vi. f. 19-21. 



Associated with P. barrisi and attached to the same card 

 marked "types" in the University of Michigan collection, 

 there is a specimen which differs from it in being a much 

 more depressed shell with a much deeper notch in the peri- 

 stome, and in having the notch at the middle of the outer 

 side of the whorl instead of in the dorsal part of the outer 



* Trans. Acad. Sci. St. Louis. 9 : 42. pl. 5. f. 1-4. — In this place the 

 author is made to state, by the omission of the word definitely, that the 

 genus has never before been recognized in America. Two species have 

 in fact been referred by their authors to the genus, — P. dubium Dawson, 

 and P. helicoides M. & W., — but neither of them is certainly or even prob- 

 ably a member of the genus. 



