GASTROPODA— STROPHOSTYLIDJE. 



679 



Medium-sized, of four volutions, very oblique through loose 

 coiling, last one partly free ; expanding rapidly, but more uni- 

 formly than in most species. 



Carbonic limestones of Missouri, Texas, and Utah. 



Fig. 949. Strophostylus carley- 

 anus. (After Whitfield, Am. Mus. 

 Nat. Hist. Bull. ) 



Fig. 950. Strophostylus nanus, a, b, 2 views ; 

 c (right), S. remex. (Ind. Surv. & Bull. 77, 

 U. S. G. S. ) 



LXXIII. Diaphorostoma Fisher. (Platyostotna Conrad.) 

 Differs from Strophostylus in the regular enlargements of the 

 whorls, the last not being ventricose ; columellar lip smooth. 

 Siluric-Devonic. 

 231. D. niagarense Hall. (Fig. 951.) Siluric. 



Fig. 951. Diaphorostoma niagarense. (After Hall.) 



Body-whorl inflated toward aperture; sutures deeply depressed; 

 3-4 volutions ; fine spiral and strong transverse striae. 



Niagaran and Guelph of New York and nearly all other 

 exposures. 

 232. D. ventricosum Conrad. (Fig. 952.) Devonic. 



Larger and more ventricose than preceding ; aperture nearly 

 circular. 



Helderbergian and Oriskanian of New York, etc. 



