1 90 1.] Gidley, The North American Species of Equus. 



115 



recent looking specimens, and from the corresponding teeth of the domestic 

 horse, in the remarlvable degree of simplicity of the enamel folding, as seen on 

 the triturating surface." 



Measurements given. 



Second upper molar (? m^) 



S Antero-posterior diameter — I4f lines (31 mm.). 

 \ Transverse " — I2| " (27 mm.). 



" (?P-^ Tvpe')-^ ^"^^'°'P°^^^"°''" ^^^ " ^32 mm.). 



V- P W ^ < Transverse " isi "(28.5 mm.). 



This species is apparently undis- 

 tinguishable from E. excelsus, as the 

 type specimens agree in size and both 

 are extremely simple in tooth pattern. 

 However, the Nebraska specimen shows 

 a tendency to a more complicated pat- 

 tern of enamel folding and may be an 

 extremely simple variation of a species 

 possessing in general more complicated 

 teeth {E. complicalus) ; while an exam- 

 ination of some teeth representing sev- 

 eral individuals from the California 

 locality, which have been identified by 

 Leidy as E. occidentalis, shows a uniform 

 simplicity of enamel folding. While 

 this is by no means to be considered 

 sufficient ground for retaining the spe- 

 cies as separate, there is nothing on the 

 other hand to prove them synonymous, 

 and as they have been named from two 

 widely different localities on opposite 

 sides of the Rocky Mountain system, it 

 is perhaps wisest to retain the two spe- 

 cies as distinct for the present. 



In 1869 ^ Dr. Leidy united these two 

 species on the ground of the absence in 

 both, of the little enamel fold, near the 

 bottom of the deep valley between the 

 protocone and the hypocone. This. 



Fig. 10. Equus occidentalis 

 Leidy. Type. Superior third 

 premolar. Ay crown view ; .'J ', 

 e.xternal view. 



' This tooth has been chosen as the type inasmuch as it was the one figured. 



^ Extinct Mammalian Fauna of Dak. and Neb., p. 267. When Leidy combined these two 

 species he retained the name E. occidentalism evidently through a mistake in the date of his 

 first description of E. excelsus, which he gives as 1868, but which should be 1858. 



