1913] 



Merriam: Horses of Eancho La Brea 



417 



shortness and width of nose, relative narrowness across the skull 

 through the anterior region of the maxillary ridges, relative 

 narrowness in superior view immediately in front of the inion, 

 and smaller size of the orbits. The postpalatine foramina and 

 the anterior end of the inferior nasal opening are somewhat 

 farther forward in some specimens than in E. niobrarensis. 



The cheek-teeth of the Rancho La Brea form are slightly 

 larger than in E. niobrarensis, and the tooth row is in most 

 specimens relatively longer. The relation of the tooth row to 

 the basilar length in the type of E. niobrarensis is 33.8%. In 

 no. 21002, a much older specimen, from Eancho La Brea, the 

 proportion is 34.9%. In no. 20098 it is 36%. 



As shown in the table of measurements on page 410, the 

 average width of the cheek-teeth of the Great Plains form is 

 somewhat less than in the average of the Rancho La Brea speci- 

 mens. Unless the difference can be shown to hold for a large 

 number of individuals it would hardly be considered of specific 

 value. Between E. niobrarensis and the Rancho La Brea form 

 there are certain small differences in the pattern of the enamel. 

 In E. niobrarensis the folding of the enamel at the anterior and 

 posterior borders of the fossettes, and at the anterior end of 

 the post-protoeonal valley is more pronounced, and in that 

 species the anterior end of the post-protoconal valley is wider. 



The relation of E. niobrarensis to the Rancho La Brea horses 

 suggests a resemblance of the former species to E. excelsus. 

 E. excelsus is apparently somewhat nearer to E. niobrarensis 

 than is the California E. Occident alis. In a recent paper Hay 1 ' 1 

 has discussed the relationships of E. niobrarensis and E. excelsus, 

 and considers them distinct. In Hay's paper a series of cheek- 

 teeth referred to E. excelsus seems partly to bridge the gap 

 between these two species, but other characters may still separate 

 them. 



The California E. occiclentalis appears to be separable from 

 E. niobrarensis by more simple pattern of the enamel of the 

 cheek-teeth, and by several skull characters, no one of which 

 seems, however, entirely reliable with the material available. 

 The presumption is that these species are distinct, but it is 



ie Hay, O. P., Proe. U. S. Nat. Mus., vol. 44 (no. 1969), p. 592, 1913. 



