$4 . F. ICHAI>. vn. 



from the United States a tooth ot 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 Spanish 

 colonists ! 



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



Eossibly of an elephant,* and of a hollow-horned ruminant, discovered 

 y 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 f 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 America strongly contrasted 

 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 armadillos. 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 antelope) of hollow-horned ruminants, of 

 which great division South America is not known to possess a single 

 species. Formerly, but within the period when most of the now 

 existing shells were living, North America possessed, besides hollow- 

 horned ruminants, the elephant, mastodon, horse, and three genera of 

 Edentata, namely, the Megatherium, Megalonyx, and Mylodon. Within 

 nearly this same period (as proved by the shells at Bahia Blanca) 

 South America possessed, as we have just seen, a mastodon, horse, 

 hollow-horned ruminant, and the same three genera (as well as several 

 others) of the Edentata, Hence it is evident that North and South 

 America, in having within a late geological period these several genera 

 in common, were much more closely related in the character of their 



* 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 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 

 Syneiheres prthensilis, 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." 



