1913] Merriam: Horses of Rancho La Brea 415 



of the enamel at the anterior end of the post-protoconal valley. 

 The tooth was characterized especially by its large size. The 

 dimensions are compared with those of E. occidentalis in the 

 table on p. 410. As is seen in the table of measurements, the 

 largest specimens from Rancho La Brea approach the type of 

 E. pacificus in dimensions. They are, however, quite different 

 in average pattern of the enamel. Even the largest speci- 

 mens from Rancho La Brea fall below the dimensions of Leidy's 

 type of E. pacificxis, and below Gidley's typical material from 

 Fossil Lake. It is very doubtful whether any of the Rancho 

 La Brea specimens thus far examined can be referred to E. 

 pacificus. It is evident that the typical horses of Rancho La 

 Brea are E. occidentalis. 



Comparison with Equus excelsus Leidy. — The Great Plains 

 species described as Equus excelsus by Leidy in 1858, from ma- 

 terial obtained in Nebraska, approaches the California E. occiden- 

 talis very closely. In reviewing the species in 1869 Leidy 10 stated 

 that there was little doubt that E. excelsus and E. occidentalis 

 were the same, and he united the two. In 1873 Leidy 11 referred 

 to the two under the name of E. occidentalis. As pointed out 

 by Gidley 12 the name E. excelsus really preceedes E. occidentalis. 

 Gidley suggests that the Nebraska form shows a tendency to 

 more complicated enamel pattern of the cheek-teeth, and that it 

 may be a relatively simple variation of a form normally with a 

 much more complicated pattern than the typically simple teeth 

 of the California E. occidentalis. Gidley also calls attention to 

 the fact that E. excelsus and E. occidentalis were described from 

 geographic stations widely separated, on opposite sides of the 

 Rocky Mountain system. After weighing the evidence available, 

 Gidley held it wisest to consider the two species as distinct. 



Recently Hay 13 has referred to E. excelsus additional mate- 

 rial, and has discussed the relation of the species to E. niobra- 

 rensis. 



10 Leidy, J., Extinct Mammalian Fauna of Dakota and Nebraska, p. 

 267, 1869. 



11 Leidy, J., Geol. Surv. Terrs., vol. 1, p. 243, 1873. 



12 Gidley, J. W., Bull. Am. Mus. Nat. Hist., vol. 14, p. 115, 1901. 



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



