i6o 



NORTH AMERICAN INDEX FOSSILS. 



Tropitoidea. 



CXI. CoLUMBiTES Hyatt and Smith. 



Evolute, discoidal, with slightly embracing whorls, gradually 



mcreasing in size; body chamber long; surface with ribs, spirals 



and frequent varices ; suture ceratitic, with divided ventral, a prin- 



FiG. 1407. a-c, Trachyceras (^Froirachyceras) lecontei, two views and suture X 

 Yz ; d-f, T. i^Anolcites) meeki, two views X Yzi and suture (/). (After Hyatt and 

 Smith.) 



cipal lateral, and an auxiliary lobe. (This genus meets require- 

 ments for ancestor of Tropites.) Triassic. 



259. C. parisianus Hyatt and Smith. (Fig. 1404,^-;.) Triassic. 



Whorls very slightly indented by preceding whorl ; sculpture 

 weak at maturity, strong in young; saddles rounded and entire; 

 first lateral lobe serrate. (Type of genus.) 



Lower Triassic (above Meekoceras beds) of southeastern Idaho. 



CXII. Sagenites Mojsisovics. 



Subglobose, somewhat compressed shells with rounded sides, 

 arched venter, narrow umbilicus, and dichotomous ribs which cross 

 the venter and are cancellated by spiral lines which often produce 

 a series of short spines (Trachysagenites Moj.) ; sutures ammo- 



