702 



NORTH AMERICAN INDEX FOSSILS. 



Coal measures of Illinois, Indiana, Ohio, Iowa, and Missouri. 



320. S. texanum Shumard. (Fig. 1010, c f d.) Carbonic. 

 Shorter and more globose ; notch strong ; columellar callus 



strong. 



Coal measures of Texas and Illinois. 



321. S. primigenium (Conrad). (Fig. 10 10, e.) Carbonic. 



FlG. ioio. a, b, Sphcerodoma mediate; c,d, S. texanum; <?, S. primigeniu?n ; f, S. 

 ponderosum. (After White, 13th Ind. Rep.) 



Larger, and with scarcely developed columellar fold ; thick 

 shell ; otherwise like preceding. 



Coal measures of Pennsylvania, Ohio, Indiana, Illinois, Iowa, 

 Missouri, and Arkansas. 

 322. S. ponderosum Swallow. (Fig. ioio,/.) Carbonic. 



Very large, with deeply sinuous inner lip but no fold ; whorls 

 convex, embracing to above ambitus. 



Coal measures of Kansas, Iowa, Missouri, and Ohio. 



Family Trochid/e Adams. 

 XC. Gibbula Risso. 

 Trochoid, rarely round-whorled, usually umbilicated shells, em- 

 bracing to ambitus, with angle and aperture rounded. Tertiary- 

 Recent. 



