152 ST. FE. Oct. 1833. 



The occurrence of the fossil horse and of Mastodon angus- 

 tidens in South America, is a much more remarkable circum- 

 stance than that of the animals mentioned above in the north- 

 ern half of the continent; for if we 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 

 6f low land on the coast, a broad barrier ; we shall then have 

 two zoological provinces strongly contrasted with each other. 

 Some few species alone have passed the barrier, and may be 

 considered as wanderers, such as the puma, opossum, kin- 

 kajou, and peccari. The mammalogy of South America is 

 characterized by possessing several species of the genera of 

 llama, cavy (and the allied animals), tapir, peccari, opossum, 

 anteater, sloth, and armadillo. If North America had pos- 

 sessed species of these genera proper to it, the distinction of 

 the two provinces could not have been drawn ; but the pre- 

 sence of a few wanderers scarcely affects the case. North Ame- 

 rica, on the other hand, is characterized by its numerous ro- 

 dents,t and by four genera of solid horned ruminants,^ of which 

 section the southern half does not possess a single species. 



whether from west to east, or the reverse. Perhaps, when we recollect 

 how extraordinarily the Pachydermata abounded during the Tertiary 

 epochs in the Old World, and that the representatives of these animals 

 now only exist in that quarter, it may seem most probable that the 

 migration took place from Asia to America. 



* This is the division followed by Lichtenstein, Swainson, and Richard- 

 son. The section from Vera Cruz to Acapulco, given by Humboldt in 

 the Atlas to Polit. Essay on Kingdom of N. Spain, will show how im- 

 mense a barrier the Mexican table-land forms. 



f Dr. Richardson (Report to Brit. Assoc, p. 157), talking of the 

 identification of a Mexican animal with the Synetheres prehensilu, says, 

 " We do not know with wliat 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." 



X Dicranocerus furcifer, Capra Americana, Ovis monlana. Bos Americana, 

 and Moschatus. — Report to Brit. Assoc, p. 159. 



