200 



NORTH AMERICAN INDEX FOSSILS. 



347. A. percostatum Gabb. (Fig. 1461.) Comanchic. 



Very large (about i^ ft. long), the early stages loosely coiled 

 into a spiral, the straight portion rapidly enlarging; internal mold 

 finely costate in the young, smooth in the subquadrate adult, but 

 with a few coarse ribs in the final crook. 



Horsetown of California. 



CLV. Hamites Parkinson. 



Gerontic ammonoids which have lost the power of coiling, 

 though curving two or three times through an angle of 180° ; 

 costse are continuous all around, and tubercles are absent; suture 

 with first lateral lobe divided in two, and saddles strongly bifid. 

 Comanchic-Cretacic. 



348. H. fremonti Marcou. (Fig. 1462.) Comanchic. 



Fig. 

 Hill.) 



1462. Hamites fremonti^ X Yt,- (After 



Fig. 1463. Hajuiles obstrictus. 

 (After Whiteaves, Mes. Foss. ) 



Costse rather coarse, with a suspicion of tuberculation on the 

 ventral margin, becoming faint or obsolete towards the dorsum. 



Washita of Oklahoma and Texas. 

 349. H. obstrictus Jimbo. (Fig. 1463.) Cretacic. 



Smaller, with more numerous and crowded, sharper ribs, sepa- 



