90 



NORTH AMERICAN INDEX FOSSILS. 



Fig. 1308. Stearoceras gibbosum, lateral and ventral views. (After Hyatt, Texas 

 Survey. ) 



107. L. chesterense Meek and Worthen. (Figs. 1309, 1310.) 



Mississippic. 



Strongly involute with deep umbilicus; whorls rounded, nar- 

 rower and less rapidly enlarging than in preceding. 



Chester of Illinois. 



Fig. 1309. Leuroceras chesterense^ umbilical view. FiG. 1310. Leuroceras chesterense, 



(After Meek and Worthen, 111. Pal., II.) ventral view. (After Meek and Wor- 



then, 111. Pal., II.) 



