PLATE X. 



LOUP FORK EPOCH. 



Molar teeth of species of ProtoMppus , natural size. 



Figure 1. Temporary dentition of colt of Frotohippus ?pachyops. Cope; from 

 skull figured in Plate XII. 



Figure 2. Frotohippus perditus, Leidy; an old deciduous and two young per- 

 manent molars, external view {d4 should he at the lower side of the 

 figure); a. grinding faces; from northeast Colorado. 



Figure 3. Temporary molars of a species of Protohippus; from Wyoming. 



Figure 4. Frotohippus fmirabilis Leidy; with dentition. 



Figure 5. Frotohippus medius. Cope; superior molars; from Cottonwood Creek, 

 Oregon. 



[110] 



