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specimen found here : he has named this American horse Equus 

 curvidens. Certainly it is a marvellous fact in the history of 

 the Mammalia, that in South America a native horse should 

 have lived and disappeared, to be succeeded in after ages by 

 the countless herds descended from the few introduced with the 

 Spanish colonists ! 



The existence in South America of a fossil horse, of the 

 mastodon, possibly of an elephant,^ and of a hollow-horned 

 ruminant, discovered by MM. Lund and Clausen in the caves of 

 Brazil, are highly interesting facts with respect to the geo- 

 graphical distribution of animals. At the present time, if we 



FOSSIL TOOTH OF HORSE, FROM BAHIA BLANCA. 



divide America, not by the Isthmus of Panama, but by the 

 southern part of Mexico ^ in lat. 20°, where the great table-land 

 presents an obstacle to the migration of species, by affecting 

 the climate, and by forming, with the exception of some valleys 

 and of a fringe of low land on the coast, a broad barrier ; we 

 shall then have the two zoological provinces of North and South 



1 Cuvier, Ossemens Fossiles, torn. i. p. 158. 



2 This is the geographical division followed by Lichtenstein, Swainson, Erichson, 

 and Richardson, The section from Vera Cruz to Acapulco, given by Humboldt in 

 the Polit. Essay on Kingdom of N. Spain will show how immense a barrier the 

 Mexican table-land forms. Dr. Richardson, in his admirable Report on the Zoology 

 of N. America read before the Brit. Assoc. 1836 (p. 157), talking of the identifica- 

 tion of a Mexican animal with the Synetheres prehensilis^ says, "We do not know 

 with what propriety, but if correct, it is, if not a solitary instance, at least very 

 nearly so, of a rodent animal being common to North and South America. " 



