194 



NORTH AMERICAN INDEX FOSSILS. 



CL. AcANTHocERAS Ncumayr. 

 Ammonites with the young discoidal, non-tuberculate, and sec- 

 tion rounded till late neanic stage; adult with straight, simple, or 



Fig. 1452. Lyticoceras hyatti, X %• (After Stanton.) 



bifurcating ribs, thickening outwards with lateral and marginal 

 tubercles ; venter with median row of tubercles ; suture deeply cut ; 

 first lateral saddle broad and bifid ; ventral lobe straight and deep, 

 with truncated siphonal saddle. Comanchic-Cretacic. 



Fig. 1453. Lyticoceras angulatus^ X ' 



( Afier Stanton. 



339. A.(?) justinae Hill. Comanchic. 



Discoidal, thin and flattened ; umbilicus large ; ribs numerous 

 with intercalated shorter ones; venter oblately rounded. 



Trinity beds of Texas. 



Mantelliceratida. 

 CLI. DouviLLEiCERAS Grossouvrc. 

 Ammonites, with the young shell discoidal, and more or less 

 sharply costate, with two or three rows of large tubercles on each 



