438 University of California Publications in Geology [Vol. 7 



postfossette are each thrown into six or more short folds. The 

 anterior wall of the prefossette also exhibits very marked 

 plications. The posterior wall of the postfossette shows at least 

 one strong fold. 



The upper cheek-teeth do not closely resemble those of any 

 AVest-American species known to the writer. In some respects 

 they show more similarity to Neohipparion plicatile of the 

 Florida Pliocene than to most of the western species. The general 

 form of the teeth, the small, round protocone, the very complexly 

 folded enamel of the fossettes, and to some extent the detailed 

 pattern of the enamel folds in the Mohave form are strikingly 

 similar to the expression of corresponding characters of the Old 

 World Hipparion species. It may be noted in this connection 

 that the American form N. plicatile, with which the Mohave 

 form has been compared, is considered by Gidley 3 as represent- 

 ing a group differing in some respects from other American 

 species and possibly belonging to an American branch of the 

 Old World Hipparion. 



In dimensions and in general form the Mohave species is very 

 near to Hipparion richthofeni of China and to the typical H. 

 H racile of Europe. The Mohave form seems distinguishable from 

 H. g racile by somewhat larger size, a more distinct tendency to 

 lateral compression of the protocone, slightly wider mesostyle 

 ribs, and possibly by very small differences in the folding of the 

 enamel walls of the fossettes. 



The resemblance of H. mohavense to H. richthofeni, as that 

 species is figured by Schlosser, 4 is very close. In the California 

 form the dimensions, cross-section of protocone, and most details 

 in the enamel pattern match closely the corresponding char- 

 acters of the Chinese species. There are small differences sug- 

 gesting separation ; as in the tendency of the small fold of the 

 inner enamel wall opposite the protocone to show two or more 

 subdivisions in most specimens of H. richthofeni, while in the 

 Mohave specimens the fold is commonly simple ; and according 



a Gidley, J. W., Bull. Amer. Mus. Nat. Hist., vol. 23, p. 905, 1907. 

 * Schlosser, M., Saugethiere Chinas, Abh. Munich Akad., Math-Ph. 

 Classe, Bd. 22, Taf. 4, 1903-6. 



