THE VOYAGE OF THE BEAGLE 143 



common in North America. Mr. Lyell has lately brought 

 from the United States a tooth of a horse; and it is an in- 

 teresting fact, that Professor Owen could find in no species, 

 either fossil or recent, a slight but peculiar curvature char- 

 acterizing it, until he thought of comparing it with my speci- 

 men 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 intro- 

 duced with the Spanish colonists! 



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

 mastodon, possibly of an elephant, 4 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 geographical distribution of animals. At the present 

 time, if we divide America, not by the Isthmus of Panama, 

 but by the southern part of Mexico 5 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 zoo- 

 logical provinces of North and South America strongly con- 

 trasted with each other. Some few species alone have 

 passed the barrier, and may be considered as wanderers from 

 the south, such as the puma, opossum, kinkajou, and peccari. 

 South America is characterized by possessing many peculiar 

 gnawers, a family of monkeys, the llama, peccari, tapir, 

 opossums, and, especially, several genera of Edentata, the 

 order which includes the sloths, ant-eaters, and armadilloes. 

 North America, on the other hand, is characterized (putting 

 on one side a few wandering species) by numerous peculiar 

 gnawers, and by four genera (the ox, sheep, goat, and ante- 



4 Cuyier. Ossemens Fossiles, torn. i. p. 158. 



8 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 Report on the Zoology of N. America read before the Brit. 

 Assoc. 1836 (p. 157), talking of the identification of a Mexican animal 

 with the Synetheres prehensilis, says, " We do not know with what pro- 

 priety, 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." 



