266 



NORTH AMERICAN INDEX FOSSILS. 



emi in its smaller size, greater gibbosity and in the more elevated 

 and incurved beak of the pedicle valve. 



Chemung of New York and Kinderhook of Iowa. 



202. R. michelini (L'Eveille). (Fig. 319, c.) Mississippi. 

 Quite similar to R. vanuxemi but differs in the parallel direction 



of the dental lamellae and in the character of the radial striae. 

 Waverly of Pennsylvania, Ohio, Kentucky, New Mexico. 



203. R. burlingtonensis Hall. Mississippi. 

 Of medium size, subcircular. Valves subequally convex. Beak 



of pedicle valve extended and cardinal area high. 

 Burlington of Illinois, Iowa, Missouri. 



204. R. dubia Hall. (Fig. 319, d-g.) Mississippi. 

 Distinguished by its small size, nearly equal convexity of the two 



valves, the prominent beak of the pedicle valve and the distinctly 

 defined sinus of the pedicle valve. 



St. Louis of Kentucky, Indiana, Illinois, Missouri, Iowa. 



205. R. pecosi (Marcou). (Fig. 321, a-c.) Carbonic. 

 Small. Length at times exceeding breadth. Pedicle valve often 



flattened toward the front and lacking a definite mesial sinus. 

 Brachial valve more convex than the pedicle valve. Radiating 

 striae crossed by fine concentric growth lines- and near the front by 

 imbricating lines. 



Throughout the Carbonic of North America. 



Fig. 321. a-c, Rhipidomella pecosi ; d-f, Schizophoria striatirfa (Ind. Geol. Surv. ) 

 g-h, S. tioga. (After Hall.) 



