54 



NORTH AMERICAN INDEX FOSSILS. 



gradually increasing in depth (6 chambers in 22 mm. with increase 

 in diameter from 9-12 mm.). Siphuncle subcentral. 



Goniatite limestone of Indiana ; Marshall of Michigan ; Waverly 

 of Ohio. 



35. 0. epigrus Hall. (Fig. 1254, a.) Mississippic. 

 Subcylindrical, very gradually tapering ; section circular ; siphun- 

 cle small; subcentral; septa slightly concave, distant about one 

 third the diameter of the shell; surface with rather faint, distant, 

 longitudinal lines. 



St. Louis (Spergen) of Indiana. 



36. 0. rushense McChesney. (Fig. 1254, 6.) Mississippic-Permic. 



i 



Fig. 1255. Protocycloceras lamarcki, sectional and exterior and end views of speci- 

 mens. (After Ruedemann, Bull. 90, N. Y. State Mus. ) 



Rather rapidly tapering; septa moderately concave; siphuncle 

 subcentral; surface finely striated. 



Waverly of Ohio ( ?) ; Lower Coal Measures of Iowa and 

 Indiana ; Permic of Texas. 



