1072 The Perissodactyla. [Dec. 
. Hippidium spectans Cope, teeth. 
from Pliocene formation of OF © 
on. Fig. a, superior molar from below; 
4, incisor ‘oie of crown, showing cup. 
Natural size. 
Fic. 40. Superior molar of Hippo- 
therium from which the cementum Oise 
has been removed, goa the 
forms of the crests, m Kowa- 
levsky 
These relations may be expressed as follows, in tabular form 
Hippotherium. Protohippus. 
Anchippus. ce 
Paloplotherium. Mesohippus. 
Anchilophus. Paleotherium. 
* 
Type with internal cusps and 
with fewer premolars like true molars. 
- Equus crenidens Cope, 
‘ F 
a 
superior molar, pattern of enamel- Fic. 43. Equus caballus Le % Gaud- 
molars. From ah 
ridges of crown. Original; from 4, ‘ee rior, true 
Pliocene epoch of Texas. Natural  Five-sixths natural size 
r Fig. 35 
