GASTEROPODS. 175 



Platyceras nasutum Miller, 1891: Geol. Sur. Indiana, 17th Ann. Rep., Adv. 

 sheets, p. S2, pi. x\v, figs. 17-18. 



Shell like that of an immature C. equilateralis, but much 

 thinner and more delicate. 



Horizon and local> ties. Lower Carboniferous, Chouteau 

 limestone, Sedalia ; Burlington limestone: Louisiana. 



The apical portion of the shell is more slender and ex- 

 tended than the tjpe would indicate from casual examination. 

 The typical specimen has the longitudinal folds much more 

 prominent than is apparent in an average example of the 

 species ; for in the majority of individuals the plications are 

 scarcely noticeable. This species is widely distributed geo- 

 graphically, and preserves its individuality remarkably over 

 its entire range. Typical specimens have been collected at 

 LeGrand, in central Iowa, at Burlington, in the southeastern 

 part of the same state, at Lodi, Ohio, and Sedalia, in west-cen- 

 tral Missouri. 



Careful comparisons of the Sedalia specimens described 

 by Miller, and those from other localities mentioned, leave 

 little room for doubt that the recently named Platyceras nasu- 

 tum is anything else than the same form noted more than 30 

 years ago, by White & Whitfield, under the title of P. para- 

 Hum. 



Capulus tribulosus ( WHITE). 



Plate liii, figs, lla-c. 



Platycerastribulosum White, 1883: U. S. Geol. Sur. Terr., 12th Ann. 



Rep. , p. 186, pi. xli, figs. 6a-b. 



Platyceras tribulosum Keyes, 1889 : Proc. Acad. Nat. Sci., Phila., p. 290. 

 Capulus tribulosus Keyes, 1890: Am. Geol., vol. VI, p. 9. 

 Capulus tribulosus Keyes, 1890: Proc. Acad. Nat. Sci., Phila., p. 170, pi. 



ii, figs. 4a-b. 



Shell rather below medium size, subspiral, rather slender, 

 forming about one volution ; regularly expanding to the aper- 

 ture. Apex incurved, far removed from the body of the shell. 

 Aperture irregularly oval ; usually more or less broadly lobed 

 posteriorly; lip sharp, irregular, with usually a deep sinus 

 anteriorly. Surface glabrate, but exhibiting numerous fine, 

 closely arranged lines of growth; also marked by three longi- 



