128 



NORTH AMERICAN INDEX FOSSILS. 



176. P. hyatti Whitfield. (Fig. 1374, a, &.) Devonic. 

 Very large, quite strongly curved in young, rapidly expanding; 



living chamber strongly constricted below the aperture. 

 Columbus limestone of Ohio. 



177. P. amphora Whitfield. (Fig. 1374, c.) Devonic. 

 Short; aperture very strongly contracted; last septa closely 



crowded. 



Columbus of Ohio (closely related forms occur in the Traverse 

 limestones of Michigan). 



178. P. eximium Hall. (Fig. 1375.) Devonic. 



Fig. 1375. Poterioceras eximium, X ] 

 (After Hall, Pal. N. Y., V.) 



Fig. 1376. Poterioceras oviforme^ X V\ 

 (After Hyatt.) 



Large, gibbous, straight, and exogastric, with subcircular or 

 very broadly oval section ; tube rapidly enlarging to living chamber 

 which is regularly contracted to aperture ; siphuncle nummuloidal. 



Onondaga of New York and Ohio. 



