CEPHALOPODA— AMMONOIDEA. 



221 



CLXVIIL Stantonoceras Johnson. 



Like Placenticeras in the young and in septa, but adult with 

 broad venter; generally strong tubercles, which sometimes become 

 extended into costae ; the genus represents the terminal members of 

 the evolutional line of Placenticeras. 

 387. S. newberryi (Hyatt). (Fig. I499-) . Cretacic. 



Fig. 1499. Stantonoceras newberryi, two views and section, \ )4, of the type. 

 (After Hyatt.) 



Placenticeras stage continued to beginning of adult; venter be- 

 comes broadly rounded ; rounded tubercles near margin and near 

 umbilicus, but becoming obsolete in adult and old age; obscure 

 fold-like costse occur. 



Upper Cretacic of Presidio del Norte, Chihuahua, Mexico. 



388. S. guadaloupae (Roemer). (Fig. 1500.) Cretacic. 

 Venter broadly convex, bordered by a line of oblique, large 



tubercles ; a second line of obliquely elongate tubercles on the side. 

 San Carlos of Texas ; Pierre of New Mexico. 



389. S. pseudocostatum D. W. Johnson. (Fig. 1 501.) Cretacic. 

 Large, final whorl subquadrangular with nearly flat venter and 



flat sides marked by oblique costse due to elongation of nodes; 

 shell passes through Placenticeras stages and through stage in 

 which it has characteristics of 5. guadaloupce. (Type of genus.) 

 Pierre of New Mexico. 



