20/50 FOSSIL TOOTH OF HORSE, FROM BAHIA BLANCA.) The existence in South America of a fossil horse, of the mastodon, possibly of an elephant (7/4. Cuvier "Ossemens Fossils" tome 1 page 158.), 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 in latitude 20 degrees, 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. |