220 



NORTH AMERICAN INDEX FOSSILS. 



Onondaga and^Hamilton of New York, Ohio, Michigan, Indiana, 

 Illinois, Kentucky, Iowa, Ontario. 



XXXIV. Strophonella Hall. 



Pedicle valve concave; brachial convex. Otherwise like Strophe- 

 odonta. Stluric-Devonic. 



88. S. patenta (Hall). (Fig. 266.) Siluric. 



Average shell i^g inches long by 1^ inches wide; very con- 

 vex. Surface covered with fine unequal radiating striae crossed by 



Fig. 266. Strophonella (?) patenta, with enlargement of surface features. 

 Hall.) 



(After 



fine concentric ones. Inner surface of valves thickly covered with 

 sharp points. 



Clinton of New York, Ohio, Indiana, Alabama. 



89. S. striata Hall. (Fig. 267.) Siluric. 



Almost flat, with fine radiating striae which increase by implanta- 

 tion. Average shell 5/% inch long and ^ inch wide. 



Niagaran of New York, Kentucky, Indi- 

 ana. 



90. S. headleyana Hall. (Fig. 268.) 



Devonic. 

 Length about three fourths the width. 

 Pedicle valve concave, especially near the 

 front and with scarcely elevated beak. Brachial valve depressed at 

 umbo and very convex toward the front. Cardinal area quite wide 

 and marked by transverse striae. Radiating striae coarse and 

 sharply elevated, increasing chiefly by implantation. 



Helderbergian of New York, Kennedy Channel and Cape Frazier 

 of the Arctic regions. 



Fig. 267. Strophonella 

 striata. (After Hall.) 



