Vol. 6] Merriam: Virgin Valley and Thousand Creek. 



265 



is represented by several specimens occuring at High Rock 

 Canon in association with a larger Merychippus and a species of 

 Hypohippus. 



Occurrence : Virgin Valley Beds at Virgin Valley and at 

 High Rock Canon, Humboldt County, Nevada. 



PLIOHIPPUSC?), sp. 



At several localities in the Thousand Creek region remains 

 were found representing an equine form much larger than the 

 Merychippus species of Virgin Valley. The heavily cemented 

 upper molars are in most of the specimens (figs. 31a and 316) 

 a little shorter than in typical species of Equus, and show the 

 strong curvature of Pliohippus. The wide enamel lakes show a 

 moderate degree of plication. These teeth correspond in general 

 with the type which is recognized by Gidley and by Matthew as 

 Pliohippus. It would not however be entirely safe to refer them 

 certainly to this group until more complete material is available. 

 They may certainly be included within the limits of Pliohippus 

 and Proiohippus taken together. 



The pattern of the enamel presents peculiarities which may 

 distinguish this form from other described species, but with the 

 fragmentary material available it is not advisable to do more 

 than characterize the type found here as apparently slightly 

 different from the known species. 



Remains of the Pliohippus type are the characteristic repre- 

 sentatives of the Equidae in the Thousand Creek Beds. 



EQUUS ('?), sp. 



At some of the localities at which teeth referred to Pliohip- 

 pus (?) were collected a number of larger equine molars (figs. 

 32a, 326, and 36) have been found in which the characters 

 approach those of Equus. The crowns are longer and straighter 

 and the fossets are relatively narrower transversely than in the 

 specimens referred to Pliohippus. The character of the enamel 

 folds on the posterior side of the prefossette and the anterior 

 side of the postfossette is different from those in the forms re- 

 ferred to Pliohippus. In most of the characters in which these 

 teeth differ from the specimens referred to Pliohippus they ap- 



