328 HISTORICAL PALAEONTOLOGY. 
Val d’Arno, near Florence. Like the preceding, it survived, 
in diminished numbers, into the earlier portion of the Post- 
Pliocene period. 
The Horses (Zgude@) are represented, both in Europe and 
Fig. 249.—A, Under surface of the skull of Rhinoceros Etruscus, one-seventh of the 
natural size—Pliocene, Italy ; B, Crowns of the three true molars of the upper jaw, left 
side, of Rhinoceros megarhinus (R. leptorhinus, Falconer), one-half of the natural size 
—Pliocene, France. (After Falconer.) 
America, by the three-toed Hipparions, which survive from the 
Miocene, but are now verging upon extinction. For the first 
time, also, we meet with genuine Horses (Zgwzs), in which 
each foot is provided with a single complete toe only, encased 
ina single broad hoof. One of the American species of this 
period (the gus excelsus) quite equalled the modern Horse 
in stature ; and it is interesting to note the occurrence of indi- 
genous horses in America at such a comparatively late geo- 
logical epoch, seeing that this continent certainly possessed 
none of these animals when first discovered by the Spaniards. 
Amongst the Even-toed Ungulates, we may note the occur- 
