CHAP. xxn. FOSSIL EQUINE SPECIES IN AMERICA. 439 



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

 the Asiatic species, R. Indicus, 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 search 

 ing 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 we could obtain from the 

 continents of Europe, Africa, and Asia. We might have pre 

 sumed that as no living representative of the equine famity, 

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

 by North 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, ac 

 cording to Dr. Leidy, representatives of five other fossil genera 

 of Solipedes. These he names, Hipparion, Protohippus, Mery- 

 chippus, Hypohippus, and Parahippus. On the whole, no less 

 than twelve equine species, belonging to seven genera (includ 

 ing the Miocene Anchitherium of Nebraska), being already 



