416 University of California Publications in Geology [Vol. 7 



With only meagre material representing' the cheek-tooth 

 dentition at hand, it seems futile to attempt to establish definitely 

 the relationship of E. excelsus to the California E. oecidentalis. 

 It is certainly necessary to have a larger series of teeth, and it 

 will probably be necessary to have good skull material before a 

 satisfactory comparison can be made. 



A character of the type of E. excelsus to which both Gidley 

 and Hay have called attention is the position of the postpalatine 

 foramina, which are unusually far forward, opposite the anterior 

 half of M 2 . In the Rancho La Brea skulls the postpalatine fora- 

 mina range from a position opposite the middle of M 3 in individ- 

 uals of advanced age to a position opposite the posterior half of 

 M 2 in individuals of middle age with all of the molars in function. 

 The type of E. excelsus represents a young adult with M 3 

 sufficiently worn to show the enamel pattern clearly. It is pos- 

 sible that the somewhat advanced position in the California form 

 may be indicative of relationship to E. excelsus. 



Comparison with Equus scotti Gidley. — Of the American 

 Pleistocene horses known up to the present time Equus scotti, 

 described by Gidley 14 , is the only form represented by more 

 than a single skull. Unfortunately only one of several skulls 

 obtained up to the time of Gidley 's revision of the Pleistocene 

 horses in 1901 was that of an adult in which all of the teeth had 

 come into full use. The Rancho La Brea horses resemble E. 

 scotti in being a large-headed form. They differ from E. scotti 

 in the somewhat smaller cheek-teeth, less pronounced enamel 

 folds around the fossettes and at the anterior end of the post- 

 protoconal valley of the cheek-teeth, and possibly also in possess- 

 ing a shorter and wider nose. Other differences will doubtless 

 appear when the two species can be more fully compared. 



Comparison with Equus niobrarensis Hay. — Hay's recently 

 described species, Equus niobrarensis 1 ' , from Hay Springs, 

 Nebraska, approaches the Rancho La Brea form closely in char- 

 acters of skull and dentition. Both types have a heavy, short 

 head, a heavy mandible, and a short, wide nose. The Rancho 

 La Brea species differs slightly from E. niobrarensis in the 



i* Gidley, J. W., Bull. Am. Mus. Nat. Hist., vol. 13, p. Ill, 1900. 

 is Hay, O. P., Proc. U. S. Nat. Mus., vol. 44 (no. 1969), p. 576, 1913. 



