CEPHALOPODA— AMMONOIDEA. 



217 



379. P. planum Hyatt. (Fig. 1492, a.) Cretacic. 

 Sides flat, shell broad at umbilicus, sloping to concave venter, 



rather abruptly rounded to umbilicus ; venter bounded by rows of 

 alternating, elongate tubercles ; surface smooth or obscurely 

 tubercled. 



San Carlos beds. Upper Cretacic, Texas, and Presidiq del Norte, 

 Mexico. 



380. P. syrtale fMorton). f Fio^. 1492, Z?-t/.) 





Fig. 1492. a, Placenticeras planum^ X Yt. '•> b-d, P. syrtale, two views, X %i ^"^ 

 suture ; e, f, P. placenta, a fragment, X /^> ^^^ suture enlarged. (All after Hyatt.) 



Differs from preceding in having two rows of rounded tubercles 

 on the sides, extended somewhat to suggest ribs, and the umbilical 

 border less abruptly rounded. 



Eutah of Alabama; Fort Worth limestone and Taylor marl of 

 Texas. 



381. P. placenta (Dekay). (Fig. 1492, ^,/.) Cretacic. 



Large, with flat venter, smooth sides or rarely tubercled, suture 

 with numerous short lobes and saddles. (Type of the genus.) 



Ripleyan of New Jersey and Alabama. 



