400 University of California Publications in Geology [Vol. 7 



the nasal region. Equus niobrarensis is distinguished from 

 Equus laurentius by its shorter and wider nose, heavier and 

 anteriorly much higher mandible. The teeth are larger and 

 wider than in Equus laurentius. From Equus scotti this species 

 seems to be distinguished by its smaller teeth. 



Before the discovery of specimens at Rancho La Brea no 

 good skulls and no complete skeletal specimens representing 

 Pleistocene horses were known from the Pacific Coast region. 



SKULL 



The eleven practically complete horse crania from Rancho La 

 Brea naturally show certain variations in form and size, but 

 they are so near together in the assemblage of their characters, 

 and present such gradations through the series, that there seems 

 good reason for considering them all as one species, and they 

 are treated by the writer as forms of a single specific type. 



The skulls from Rancho La Brea equal or exceed those of 

 the Recent Equus caballus in size. Compared with E. caballus 

 the face is relatively a little wider, and the nose is relatively 

 short and wide. The notch between the nasals and premaxillaries 

 is wider or less acute posteriorly than in E. caballus. In profile 

 the superior fronto-nasal surface is generally nearly flat, or very 

 slightly concave above the middle of the nasals. Between the 

 orbits the frontal region is in most specimens slightly more 

 convex transversely than in E. caballus. This seems to be true 

 in stages ranging from young adnlts to individuals of fairly 

 advanced age. The nasals are relatively wide, and their anterior 

 ends reach forward to a point a little behind the superior 

 canines. 



The orbits are near the size of those in E. caballus, but tend 

 to be slightly larger. They are noticeably smaller than in E. 

 niobrarensis and E. laurentius. 



The occiput is higher and narrower than in the domestic 

 horse, and the overhang of the inion is considerably greater. The 

 greatest width across the condyles averages relatively smaller 

 than in E. caballus. 



