CHAP. XXII. FOSSIL EQUINE SPECIES IN AMERICA. 439 



the Niobrara Valley, Dr. Leicly describes a rhinoceros so like 

 the Asiatic sj)ecies, R. Indiciis, that he at first referred it to 

 the same, and, what is most singular, he remarks generally of 

 the Pliocene fauna of that part of North America, that it is 

 far more related in character to the post-pliocene and recent 

 fauna of Europe than to that now inhabiting the American 

 continent. 



It seems indeed more and more evident that when we 

 speculate in future on the pedigree of any extinct quadruped 

 which abounds in the drift or caverns of Europe, we shall 

 have to look to North and South America as a principal 

 source of information. Thirty years ago, if we had been 

 searching for fossil types which might fill up a gap between 

 two species or genera of the horse tribe (or great family of 

 the Solipedes), we might have thought it sufficient to have got 

 together as ample materials as wo could obtain froni the 

 continents of Europe, Africa, and Asia. We mighl^have pre- 

 sumed that as no living representative of the equine family, 

 whether horse, ass, zebra, or quagga, had been furnished 

 by JSTorth or South America when those regions were first 

 explored by Europeans, a search in the transatlantic world 

 for fossil species might be dispensed with. But how different 

 is the prospect now opening before us ! Mr. Darwin first 

 detected the remains of a fossil horse during his visit to 

 South America, since which two other species have been met 

 with on the same continent, while in North America, in the 

 valley of the Nebraska alone, Mr. Hayden, besides a species 

 not distinguishable from the domestic horse, has obtained, 

 according to Dr. Leid}^, representatives of five other fossil 

 genera of Solipedes. These he names Hipparion, Proto- 

 hippus, Merychippus, Hypohippus, and Parahippus. On the 

 whole, no less than twelve equine species, belonging to seven 

 genera (including the Miocene Ancliitherium, of Nebraska,) 



29 



