404 University of California Publications in Geology [Vol. 7 



anteriorly. The inferior border is usually distinctly convex 

 below the anterior cheek-teeth, and may show a slightly concave 

 region below the posterior molars. 



The anterior palatine foramina are situated much as in E. 

 caballus. In some specimens they are relatively and absolutely 

 shorter than in the domestic horse. The posterior palatine fora- 

 mina are situated near the posterior end of M 2 in animals of 

 middle age, and near the middle or anterior end of M 3 in old 

 individuals. The palatine notch of the posterior nares is oppo- 

 site the anterior half of M 2 in specimens of young adults, and 

 extends forward approximately to a line joining the middle 

 region of the second upper molars in individuals of advanced 

 age. In E. caballus this opening is somewhat shorter and wider, 

 and does not reach as far forward in the palate. 



The infraorbital formamina are commonly situated in ad- 

 vance of the anterior end of the maxillary ridges and above 

 P 3 . In no case do the maxillary ridges extend forward beyond 

 the infraorbital foramina as may occur in some forms of Equus. 



The mental foramina are approximately opposite the pos- 

 terior end of the symphysis. 



DENTITION 



The dentition is represented by a series of specimens ranging 

 from unworn milk teeth to those of old individuals in which the 

 enamel folds of the fossettes and valleys have disappeared 

 through wear. Variations in size and in enamel pattern of the 

 cheek-teeth are considerable. There is, however, such a grada- 

 tion in the teeth that there seems good reason for considering 

 all of the specimens represented as a single species. 



The incisors, where observed, are large. The lower incisors 

 in no. 21000. an old individual, are especially wide. In none 

 of the specimens available does the third lower incisor show 

 evidence of formation of an inner fold or cup. The third upper 

 incisor always shows a strongly marked cup. 



The canines are of moderate size compared with those of 

 Equus caballus. In young individuals the crown shows distinct 

 lateral compression. 



