212 NORTH AMERICAN INDEX FOSSILS. 



Placenticeratida. 



CLXIII. Protengonoceras Hyatt. 



Compressed shells, like Engonoceras, with venter deeply con- 

 cave and bordered by sharp, smooth ridges ; surface smooth, ex- 

 cept in gerontic stages when folds appear; suture simple, ceratitic, 

 with broad, flat saddles, and few marginals in the lobes. Coman- 

 chic-Cretacic. 



368. P. gabbi (Bohm). (Fig. i486.) Comanchic. 



Smooth, sides gently arched, slightly concave near venter; ven- 



FlG. i486. Protengono, 



^ 



bi : a, ventral, b, section views, X %>^^^ ^> suture. 

 (After Hyatt.) 



tral groove broad and deep; saddles low and broad; lobes with 

 three or four short marginals. 



Fredericksburg of Sonora, Mexico. 



CLXIV. Engonoceras Neumayr. 



Compressed shells, generally ornamented by nodose or fold-like 

 costse, which are often mere swellings; venter flat or concave; 

 umbilicus small or absent; sutures very simple (through retarda- 

 tion), ceratitiform, with numerous saddles and narrow lobes which 

 sometimes have numerous marginals or notches at the base ; young 

 like adult of Protengonoceras. Comanchic. 



369. E. gibbosum Hyatt. (Fig. 1487, J-/.) Comanchic. 



Venter flat, and rather broad, bordered by elongate, alternating 



nodes; a second row of obscure nodes occurs in the middle of the 



