DAKOTA AND NEBRASKA. 265 



Cuvier observes : " J'ai compart avec soin les squelettes de plusieurs varidt^s de 

 chevaux, ceux de mulet, d'ane, de zebre, et de couayga, sans pouvoir leur trouver de 

 caractere assez fixe pour que j'osasse hasarder de prononcer sur aucune de ces especes, 

 d'apres un os isole ; la taille meme ne fournit que des moyens incomplets de distinc- 

 tion, les cheveux et les anes variant beaucoup a cet egard, a cause de leur etat de 

 domesticite ; leurs differences pouvant presque aller du simple au double, et quoique 

 je n'aie pu encore m^ procurer le squelette de I'hemione ou dzigguetai, je ne doute 

 point qu'il ne ressemble autant a toutes les autres especes qu'elles se ressemblent 

 entre elles." In referring to the common Equus fossilis of Europe, the same authority 

 remarks : " La meme resemblance paroit avoir eu lieu de I'espece fossile aux especes 

 vivantes."* 



In confirmation of Cuvier's remarks, Hensel observes : " Auch mir ist es nicht 

 gelungen in den oberen Backenzahnen bestimmte Charaktere fiir die einzelnen 

 Species aufzufiuden, obgleich ich mit Ausnahme des Equus montanus alle derselben 

 vergleichen konnte."f This observation is the more important from the fact that 

 the extinct species of horses that have been indicated have been mainly distinguished 

 from differences in the upper molar teeth. 



Under the circumstances above considered, I repeat that I cannot avoid the suspi- 

 cion that the fossil remains of horses indicated as having been discovered in the 

 United States reallj' represent two distinct species, — one about the size of the ordi- 

 nary varieties of the Domestic Horse, with the bones and teeth, so far as we are 

 acquainted with them, undistinguishable from those of the latter; and a second of 

 comparatively large size (about the size of the English Dray Horse), with molar teeth, 

 but especially the upper ones, presenting on the triturating surface an unusually 

 complex folding of the enamel. To the former belongs the name of Equus fraiernus, 

 to the latter that of E. complicatus, or E. major of Dekay. 



If the remains referred to E. fraternus be regarded as belonging to the same species 

 as the existing E. cabcdhjLs, it follows that the latter was indigenous to this continent 

 at a former geological period, then became extinct, and ages subsequently was re- 

 introduced from Europe. Or, going a step further, if we are to consider E. fraternus 

 of the United States, E. curvidens of South America, and E. fossilis of Europe and 

 Arctic America the same as E. caballus of the present period, we have presented to us 

 a' remarkable instance of the distribution of a species through time and space, the like 

 of which I believe has no known parallel case among mammals. 



* Ossemens Fossiles, 4 ed., t.iii, p. 217. 



tPhysikal. Abhandl. d. K. Akad. d. Wissenschaften zu Berlin, 1860, page 85. 



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