736 



NORTH AMERICAN INDEX FOSSILS. 



V 



^ 



FlG. 1070. Turritella cumber- 

 landia. (Md. Survey.) 



FlG. 1 07 1, a, Turritella perattenuata, 

 X|; b, T. apicalis, Xl.8; c, T. suban- 

 nulata X 2 K- 



strong rounded, commonly cancellated, spiral above the basal 

 angulation, and a stronger double or triple one at a similar dis- 



