176 



NORTH AMERICAN INDEX FOSSILS. 



umbilicus bounded by a row of small, transversely elongate nodes, 

 which in large individuals bifurcate and form a series of distant, 

 more or less obscure cost^e, increased by intercalation and extend- 

 ing over the venter; septa less complex than preceding. 



Ripleyan of New Jersey and Texas; Montanan of Nebraska, 

 Dakota and Wyoming. 



SCAPHITIDA. 



CXXXL ScAPHiTES Parkinson. 



Phylogerontic ammonites with last whorl becoming more closely 

 coiled, and often making one or more nearly rectangular turns; 

 aperture generally somewhat contracted; surface marked by ribs, 

 commonly bifurcating and extending across the venter, and fre- 

 quently by two or more rows of tubercles ; suture sometimes very 

 simple, at other times with moderately incised saddles ; young like 

 Pachydiscus. Cretacic. 



295. S. warreni Meek and Hayden. (Fig. 1427,0,6.) Cretacic. 



Fig. 1427. 



(2, Scaphites ivarreni, X. % ', ^, septum enlarged ; c, Scaphites vermi- 

 formis, X %• (After Stanton.) 



Small, last whorl partly free, recurved ribs simple, alternating 

 coarse and fine ; adult suture very simple. 



Benton shales of South Dakota, Wyoming, Colorado and New 

 Mexico. 



296. S. vermif ormis Meek and Hayden. ( Fig. 1427, c. ) Cretacic. 



More nearly circular; ribs in last whorl bifurcating about the 

 middle of the side; with node at bifurcation and intercalated ribs 

 between the bifurcated pairs on the venter. 



Fort Benton of the Upper Missouri region. 



