1833.] ZOOLOGY OF NORTH AND SOUTH AMERICA. 131 
ruminant, discovered by MM. Lund and Clausen in the caves of 
Brazil, are highly interesting facts with respect to the geo- 
graphical 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 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 wander- 
ers from the south, such as the puma, opossum, kinkajou, and pec- 
cari. South America is characterized by possessing many peculiar 
gnawers, a family of monkeys, the Ilama, peccari, tapir, opossums, 
and, especially, several genera of Edentata, the order which in- 
cludes 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 ele- 
phant, mastodon, horse, and three genera of Kdentata, namely, 
the Megatherium, Megalonyx, and Mylodon. Within nearly this 
same periods (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 terrestrial inhabitants than they now are. 
* 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 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.’ 
