GASTROPODA— BELLEROPHONTIDM. 



611 



Small, generally not more than -^ in. in diameter; whorls 

 strongly involute, surface with growth lines. 

 St. Croix sandstone of Wisconsin. 



XL Protowarthia U. and S. 

 Bellerophon shells with aperture large but not abruptly ex- 

 panded ; bilobate or deeply lobed outer lip, but no slit band ; and 

 when perfect, fine revolving and transverse striae. Umbilicus 

 mostly small. Ordovicic-Devonic. 

 29. P. rectangularis U. and S. (Fig. 817, a-c.) Ordovicic. 



Fig. 817. a-c, Protowarthia rectangularis ; d-f, P. pervoluta ; g-i> P. 

 cancellata. (After Ulrich, Pal. Minn. ) 



Abruptly rounded dorsally, with small umbilicus and deep mar- 

 ginal sinuation, the lobes of which are rectangular. 



Stones River group of Minnesota, Wisconsin, and Illinois. 



30. P. pervoluta U. and S. (Fig. 817, d-f.) Ordovicic. 

 Dorsum rounded, emargination moderate, lateral lobes of lip 



rounded. 



Black River and lowest Trenton of Kentucky and Black River 

 of Minnesota. 



31. P. cancellata Hall. (Fig. 817, g-i.) Ordovicic. 

 Regularly rounded dorsum with minute umbilicus and only 



moderately expanding lip. Sinus deep and more nearly U-shaped. 

 Surface beautifully cancellated by transverse and revolving striae. 

 Trenton to Richmond of New York, Canada and throughout 

 the Middle States, chiefly in the Trenton. 



