GASTBROP ODS. 155 



Shell very small, depressed, spire scarcely elevated above 

 body whorl; volutions about four in number, moderately con- 

 vex above and below, but sharply rounded at the periphery, 

 slightly turned inward in the umbilical region ; suture linear, 

 not impressed ; aperture transversely suboval, somewhat flat- 

 tened on the inner side below. Surface glabrate. 



Horizon and localities. Upper Carboniferous, Lower Coal 

 Measures : Clinton ( Henry county). 



Trochonema umbilicata (HALL). 



Pleurotomaria umbilicata, Hall, 1847: Pal. New York, vol. I, p. 43. 

 Trochonema umbilicata Salter, 1859: Canadian Org. Remains, Dee. VII, 



p. 27. 



Trochonema umbilicata Hall, 1862: Geol. Sur. Wisconsin, p. 440. 

 Trochonema umbilicata Meek & VVorthen, 1868: Geol. Sur. Illinois, vol. 



Ill, p. 314, pi. iii, figs. 5a-b. 



Shell subconical, wider than high ; whorls about three in 

 number, with four revolving annulations; aperture obovate. 

 Surface smooth, or with lines of growth moderately prominent. 



Horizon and localities. Lower Silurian, Trenton lime- 

 stone : Pike county. 



Genus Straparollus MONTFORT. 



The generic relations of Straparollus and Euomphalus have 

 long been a subject of controversy. And, while the question 

 cannot at present be regarded as definitely settled, the evi- 

 dence derived from all available sources points to the co exten- 

 sion of the two genera. The two terms are of common occur- 

 rence in the literature of American Palaeontology, and have 

 been applied indifferently both to planorbiform gasteropod 

 shells having angulated whorls, and those possessing rounded 

 volutions. The latter features were originally regarded as dis- 

 tinctive. Yet the multiplicity of forms manifestly belonging to 

 the group founded by Montfort, has given rise to the estab- 

 lishment of a number of genera which can now be considered 

 only as of little or no utility, and seem best disposed of when 

 placed in the synonymy of this genus. Aside from the two 

 leading sections, however, these various terms require no fur- 

 ther reference here. Each name was primarily proposed for a 



