GASTROPODA— BELLEROPHONTIDJE. 



619 



53. B. platystoma Meek and Worthen. (Fig. 829, d-g.) 



Ordovicic. 

 Whorls subtriangular, gradually expanding to aperture, which 

 expands more rapidly ; umbilicus rather large. 

 Trenton (Galena) of Illinois and Minnesota. 



54. B. exiguus Foerste. Siluric. 

 Small, umbilicus minute, lip expanding, emarginate aperture 



subtrigonal, carina rounded ; lines of growth strong. 

 Clinton of Ohio, Indiana. 



55. B. pelops Hall. (Fig. 830.) Devonic. 



FiG. 830. Bellerophon pelops, three views. (After Hall.) 



Subglobose, non-umbilicate, aperture expanded, with moderate 

 sinus, and broadly rounded lobes on either side. Keel narrow, 

 sharp ; lines of growth marked. 



Schoharie and Onondaga of New York, Ohio, etc. 

 56. B. newberryi Meek. (Fig. 831, c.) Devonic. 



FiG. 831. a, b y Bellerophon propinquus ; c. B. newberryi. 

 (After Meek, Pal. Ohio, I.) 



Smaller than preceding, less expanding ; surface striae more 

 pronounced and rib-like. In the closely related B. propinquus 

 Meek (Fig. 831, a, b) t the striae are more crowded and the dorsal 

 keel has a median impression. In worn specimens the keel in 

 both may be obsolete. 



Columbus (Onondaga) limestone of Ohio. 



