670 



NORTH AMERICAN INDEX FOSSILS. 



between which and the peripheral band is a nearly flat, sloping 

 surface. Last whorl often partially loosened. 



Trenton of Canada, New York, Kentucky, Tennessee, Wiscon- 

 sin, and Illinois. Several varieties are recognized. 



Fig. 927. Trochonema beloitense. \ After Ulrich, Pal. Minn.) 



202. T. beloitense Whitf. (Fig. 927.) Ordovicic. 



More rapidly expanding, higher volutions, thicker test, coarser 



surface markings, more prominent angles, and smaller umbilicus. 



Fig. 928. a, b, Trochonema vagrans; c f d, T. {Eunema) nitidum ; e, f, T. {Gyro- 

 nema) pulchellum ; g,h } T. (Gyronema) duplicatum. (After Ulrich, Pal. Minn.) 



Stones River of Minnesota, Wisconsin, and Illinois. 



203. T. vagrans U. and S. (Fig. 928, a, b.) Ordovicic. 

 Similar to T. beloitense, but whorls somewhat more slender, and 



the last more than half free. 



Stones River group, Minnesota. 



204. T. (Eunema) nitidum Ulrich. (Fig. 928, c, d.) Ordovicic. 



