158 



NORTH AMERICAN INDEX FOSSILS. 



Middle Triassic of West Humboldt Range, Nevada, and Shasta 

 County, California (?). 



253. C. (Gymnotoceras) blakei (Gabb). (Fig. 1405, d-^.) Triassic. 



Whorls deeply embracing; venter with median keel; surface with 

 strong, dichotomous ribs dividing one third of distance from um- 

 bilicus and bending sharply forward, ending at ventral keel ; sutures 

 with slightly notched saddles. 



Middle Triassic of West Humboldt Range, Nevada. 



CVni. AcROCHORDicERAS Hyatt. 



Moderately involute, with whorls robust, laterally compressed, 

 higher than wide ; moderately wide and deep umbihcus, with abrupt 

 umbilical shoulders ; surface with strong ribs bundled on umbilical 

 knots, continuing across venter ; sutures complex, ceratitic, with 

 'rounded saddles, but notched lobes, the lobes running high up on 

 the side. Triassic. 



254. A. hyatti Meek. (Fig. 1406, a-c.) Triassic. 



Fig. 1406. a-c, Acrochordiceras kyatH,y^%, aLndiSXxiVirt', d-h, Clioni/es {Tras- 

 kites) robustus, adult {d, e) and young (/, g), X %» ^nd adult suture (//). (After 

 Hyatt and Smith. ) 



Venter highly arched and broadly rounded ; height of last whorl, 

 one half diameter of shell. (Type of genus.) 

 Middle Triassic of Nevada. 



