166 ST, FE. 



scrupulous care in ascertaining that it had been 

 embedded contemporaneously with the other re- 

 mains ; for I was not then aware that amongst the 

 fossils from Bahia Blanca there was a horse's tooth 

 hidden in the matrix, nor was it then known with 

 certainty that the remains of horses are common in 

 North America. Mr. Lyell has lately brought 

 from the United States a tooth of a horse ; and it 

 is an interesting fact, that Professor Owen could 

 find in no species, either fossil or recent, a slight 

 but peculiar curvature characterizing it, until he 

 thought of comparing it with my 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 Span- 

 ish 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 high- 

 ly interesting facts with respect to the geographi- 

 cal disti'ibution of animals. At the present time, 

 if we divide America, not by the Isthmus of Pana- 

 ma, but by the southern part of Mexicot in lat. 20°, 

 where the great table-land presents an obstacle to 



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



t 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 Re- 

 port on the Zoology of N. America, read before the British Assoc, 

 1836 (p. 157), talking of the identification 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. 



