212 



NORTH AMERICAN INDEX FOSSILS. 



cardinal extremities. Alternation of striae very pronounced on 

 both valves. 



Trenton-Lorraine of New York, Ohio, ^Indiana, Illinois, Missouri, 

 Wisconsin, Minnesota, Manitoba, Anticosti. 



Fig. 251. Rnfinesquina alternata, ventral and dorsal views, X *• (Ind. Geol. Survey.) 



70. R. deltoidea (Conrad.) Ordovicic. 

 Pedicle valve abruptly deflected at the margin except a small 



portion in front. Surface of the valve before deflection covered 

 with many irregular concentric wrinkles crossed by radiating 

 striae which, with the exception of one or two prominent ones in 

 the middle of the shell, are equal. Can be distinguished externally 

 from Leptczna rhomboidalis by its usually deltoid outline and by 

 the lesser prominence of its corrugations. 



Trenton and Utica of New York, Iowa, Missouri, Wisconsin, 

 Minnesota, Ontario, Manitoba. 



71. R. minnesotaensis (N. H. Winchell). (Fig. 252.) Ordovicic. 

 Very similar to R. alternata in form and surface features but 



usually distinguishable by its smaller size and greater convexity. 

 Trenton of Kentucky, Tennessee, Iowa, Wisconsin, Minnesota. 



Fig. 252. Rafinesquina minnesotaensis (var. inquassa), ventral and profile views]© f 

 a shell, and interior of brachial valve, X *• (Min. Geol. Survey.) 



XXXII. Stropheodonta Hall. 

 Very similar to Rafinesquina but with cardinal margins finely 

 denticulate, 1. e., marked by transverse bars which articulate as 

 teeth and pits. Shell structure coarsely punctate. . Siluric-Devonic. 



