3 8o 



NORTH AMERICAN INDEX FOSSILS. 



1 6. 0. subnasutum (Meek and Worthen). (Fig. 482, b-c.) 



Ordovicic. 

 Cardinal and basal margins slightly diverging and curving. 

 Concentric undulations irregular. 

 Galena : Illinois, Minnesota. 



17. 0. canaliculatum Ulrich. (Fig. 482, d-e.) Ordovicic. 

 Differs from other species in the strong, channel-like depression 



of the hinge line, the nearly parallel cardinal and basal margins, 

 the rounded posterior margin, and in the peculiar pallial line 

 which consists (on the internal molds) of a straight row of obscure 

 pustules extending backward from the base of the anterior 

 adductor scar. 



Cincinnati Group : Ohio, Indiana, Minnesota ; Trenton of New 

 Jersey. 



X. Grammysia de Verneuil. 



b -H^ d 



Fig. 485. a, Grammysia ovata ; b, G. bisidcata ; c, d, G. globosa. (Pal. N. Y. , V. ) 



Beaks prominent and incurved, anterior to middle. Escutcheon 

 and lunule well defined. Valves often traversed from beak to base 



