378 



NORTH AMERICAN INDEX FOSSILS. 



terior basal margin. Surface marked with concentric striae. Hinge 

 without teeth. Pallial line simple. Ordovicic-Devonic. 



9. 0. undulata Conrad. (Fig. 480.) Devonic. 

 Posterior end nearly vertically truncate. Surface marked by 



distinct undulations anteriorly and posteriorly. 



Hamilton of New York and Pennsylvania ; also Ithaca of New 

 York. 



10. 0. carinata Conrad. (Fig. 477,/.) Devonic. 

 Posterior end doubly emarginate. Postero-cardinal slope longi- 

 tudinally ridged. 



Hamilton : New York, Pennsylvania. 



VII. Cuneamya Hall and Whitfield. 

 Differs from Grammysia in that the hinge plate is weak and with- 

 out teeth. A shallow median furrow usually present. Ordovicic. 



n. C. miamiensis Hall and Whitfield. (Fig. 481.) Ordovicic. 



Fig. 481. Cuneamya miamiensis. (Pal. Ohio, II.) 



Posterior end acutely rounded. 

 Cincinnati Group : Ohio, Indiana. 



12. C. truncatula Ulrich. (Fig. 482, a.) 



Anterior end truncate. Median furrow broad. 

 Middle Galena of Minnesota. 



Ordovicic. 



FlG. 482. a, Cuneamya truncatula, internal mold of right valve ; b, c, Orthodesm a 

 subnasutum ; d, e, O. canaliculatum, right and dorsal views. (Ulrich, Minn. Pal.) 



