218 



NORTH AMERICAN INDEX FOSSILS. 



'■<•;■;■; 



Fig. 261. Stropheodonta concava, lateral and dorsal view of exterior of complete 

 shell ; and lateral and front view of interior of brachial valve showing bilobed cardinal 

 process, muscular scars; dental sockets, and crenulations of the hinge line, X '• 

 (After Hall.) 



Fig. 262. Stropheodonta 

 inaquistriata, pedicle valve, 

 X 1. (After Hall.) 



Onondaga -Chemung. Widely distrib- 

 uted throughout North America. 

 86. S. arcuata Hall. Devonic. 



Hinge line scarcely equalling greatest 

 width of shell below. Pedicle valve very 

 arcuate with sometimes an undefined ele- 

 vation along the center; cardinal extrem- 

 ities usually a little recurved, delthyrium 



