CEPHALOPODA— AMMONOIDEA. 



163 



helmet-shaped with rounded venter, and smooth surface, except 

 tor periodic varices ; sutures ammonitic with numerous similar 

 lobes and saddles. Triassic. 



264. A. andersoni Hyatt and Smith. (Fig. 1410,0^^.) Triassic. 

 Globose whorls deeply indented, umbilicus narrow, apparently 



closed in age ; umbilical shoulders abruptly rounded ; surface 

 smooth but with about four constrictions. 



Upper Triassic of West Humboldt Range, Nevada. 



265. A. (Proarcestes) pacificus Hyatt and Smith. (Fig. 1410, d.) 



Triassic. 

 Umbilicus almost closed ; general character like preceding but 



Fig. 1410. a-c, Arcestes andersoni^ X /^> ^"^^ suture; d, A. {Proarcestes') paci- 

 ficus, suture; <?,/", Ussuria waageiii, X /^> and suture. (After Hyatt and Smith.) 



suture with broader saddles, less deeply digitate. Inner and outer 

 whorls alike. 



Upper Triassic of Shasta County, California. 



CXVn. JoANNiTES Mojsisovics. 



Subglobose, laterally compressed shells, involute ; inner coils 

 completely covered by outer; umbilicus narrow and often closed 

 by callus; surface smooth but with numerous varices; septa of 

 Arcestes type, but saddles bifid and deeply digitate. Triassic. 



266. J. nevadanus Hyatt and Smith. Triassic. 



In general aspect hke Arcestes andersoni, but more compressed 



