414 University of California Publications in Geology [Vol. 7 



specimen found in Pleistocene auriferous gravels at a depth of 

 thirty feet below the surface in Tuolumne County, California. 

 Better material from an asphalt bed near Buena Vista Lake in 

 the southern end of the Great Valley of California was after- 

 ward referred to this species by Leidy 7 . The second species, 

 Equus pacificus Leidy 8 , was based upon an upper premolar tooth 

 from Martinez, California. Gidley 9 recognizes this species as 

 the common horse of the Pleistocene at Fossil Lake, Oregon. 

 These two species have come to be well known in palaeontologic 

 literature as representing the Pacific Coast horses, though rela- 

 tively meagre information has been available concerning both 

 forms. 



The cheek-teeth from Tuolumne County, California, consti- 

 tuting Leidy 's type of Equus occidentalis agree very closely in 

 dimension and in enamel pattern with average specimens from 

 Rancho La Brea. Considering that the typical Equus occi- 

 dentalis occurs in approximately the same geographic region as 

 the asphalt forms, there seems every reason to believe that the 

 common horses from Rancho La Brea represent Equus occi- 

 dentalis. The material from near Buena Vista Lake in the 

 southern end of the Great Valley of California, which Leidy 

 referred to Equus occidentalis, seems quite certainly to repre- 

 sent the same species as the specimens from Rancho La Brea. 



In the table of measurements on p. 410, the dimension of 

 Rancho La Brea specimens are shown in comparison with those 

 of the type of Equus occidentalis. 



Comparison with Equus pacificus Leidy. — The relation of the 

 Rancho La Brea horses to the type described from Martinez, 

 California under the name of Equus pacificus is not so easily 

 determined as is their affinity to E. occidentalis. The type of E. 

 pacificus as described by Leidy consisted of a single upper pre- 

 molar three, which was not figured. The enamel is described as 

 less simple than in the horses of the group referred to E. occi- 

 dentalis of California, and there was stated to be an inflection 



i Leidy, J., Extinct Mammalia of Dakota and Nebraska, p. 267, 1869. 

 Also Geol. Surv. Terrs., vol. 1, p. 242, pi. 33, fig. 1, 1873. 

 s Leidy, J., Proc. Acad. Nat. Sc. Philad., 1868, p. 195. 

 9 Gidley, J. W., Bull. Am. Mus. Nat. Hist., vol. 14, p. 116, 1901. 



