674 



NORTH AMERICAN INDEX FOSSILS. 



212. N. ventricosa Norwood and Pratten. (Fig. 934.) 



Mississippic-Carbonic. 



Whorls rapidly enlarging, last one ventricose -elongate, and 

 strongly concave below the suture. 



Archimedes limestone of Illinois ; Coal measures of Indiana 

 and Missouri. 



213. N. altonensis McChesney. (Fig. 935.) Carbonic. 

 Larger than the preceding, spire more sunken, body whorl more 



rounded, concavity proportionately less broad and at greater angle 

 with axis of shell. Var. giganteus M. and W. is larger and con- 

 cave shoulder broader. 



Coal measures of Illinois and New Mexico. 



214. N. torta(Meek). (Fig. 936.) Carbonic. 



Fig. 935. Naticopsis alto- 

 nensis. ( After Meek and 

 Worthen, 111. Geol., V.) 



Fig. 936. Naticopsis torta. (After 

 Meek, Ohio Pal., II.) 



Early whorls close-coiled, adult whorls loose ; aperture circular, 

 a slight rounded ridge on the outer part of the last whorl, and a 

 faint flattening above is observable. 



Coal measures of Ohio. 



LXIX. Trachydomia M. and W. 

 Like Naticopsis, but with nodose surface. Devonic ?-Carbonic. 



215. T. (?) praecursor (Clarke). (Fig. 937.) Devonic. 

 Early whorls round, adult flattened and angulate below ; adult 



ornamentation of numerous regular spiral rows of nodes. 



Portage (Naples) and Chemung of New York, Maryland, etc. 



216. T. wheeleri (Swallow). (Fig. 938.) Carbonic. 

 Rapidly-enlarging whorls, body whorl gibbous, aperture sub- 



