2l8 



NORTH AMERICAN INDEX FOSSILS. 



382. P. whitfieldi Hyatt. (Figs. 1493, 1494- ) Cretacic. 



Like preceding, but more involute, venter narrower throughout, 



and less completely rounded in old age ; surface without tubercles ; 



sutures more complicated in young, and more overlapping than in 



1493. Flaceniiceras whitfieldi, 

 (After Meek.) 



, small 



specirr 



Fig. 1494. Placenti- 

 ceras whitfieldi y front 

 view of specimen, Fig. 

 1493. (After Meek.) 



P. placenta; saddles almost linear from development of lobes, 

 which are very long and narrow. 



Pierre of Nebraska, South Dakota and Colorado. 



383. P. intercalare Meek. (Fig. 1495.) Cretacic. 



With two rows of tubercles as in P. syrtale, but more com- 

 pressed, tubercles smaller, less prominent, and more distant, not 

 suggestive of ribs as in that species ; venter narrow, concave, bor- 

 dered by compressed tubercles in alternating position ; suture with 

 deeper and more numerous marginal incisions. 



Pierre of Black Hills, etc. 



