84 



NORTH AMERICAN INDEX FOSSILS. 



Onondaga of New York, Ohio, and Kelley's Island, Lake Erie. 



94. R. spinosum (Conrad). (Fig. 1301.) Devonic. 



Loose and open gyroceracones of more than one volution, of 

 subcircular section; expansions in the form of tubular spines, 

 which make two ventral ridges, and often an additional one on 

 either side, when the section becomes subhexagonal. 



Schoharie of New York. 



95. R. columbiense Whitfield. (Fig. 1302.) 



Devonic. 



Fig. 1302. Ryticeras columbiense, Y^y-x,. (After Whitfield. ) 



Similar to R. cyclops, but smaller, with more rapidly increasing 

 and more closely coiled volutions which are in contact and of nearly 

 circular section; shell apparently without the foliate expansions 

 characterizing most of the species. 



Columbus limestone of Ohio. Common. 



Rhadinoceratida. 



XXX. Nephriticeras Hyatt. 



{Nautilus in part of authors.) 



Nautilicones in adult, gyroceracones in young, with elliptical or 

 broad, kidney-shaped whorl section; umbilicus large; siphuncle 



