to Iceland. But on a close
inspection of the arctic mammalia, it has been found of late years that
a very small number of the American species are identical with those of
Europe or Asia. The genera are, in great part, the same or nearly
allied; but the species are rarely identical, and are often very unlike,
as in the case of the American badger and that of Europe. Some of the
_genera_ of arctic America, such as the musk ox (_Ovibos_), are quite
peculiar, and the distinctness of the fauna of the great continents goes
on increasing in proportion as we trace them southwards, or as they
recede farther from each other, and become more and more separated by
the ocean. At length we find that the three groups of tropical mammalia,
belonging severally to America, Africa, and India, have not a single
species in common.

The predominant influence of climate over all the other causes which
limit the range of species in the mammalia is perhaps nowhere so
conspicuously displayed as in North America. The arctic fauna, so
admirably described by Sir John Richardson, has scarcely any species in
common with the fauna of the state of New York, which is 600 miles
farther south, and comprises about forty distinct mammifers. If again we
travel farther south about 600 miles, and enter another zone, running
east and west, in South Carolina, Georgia, Alabama, and the contiguous
states, we again meet with a new assemblage of land quadrupeds, and this
again differs from the fauna of Texas, where frosts are unknown. It will
be observed that on this continent there are no great geographical
barriers running east and west, such as high snow-clad mountains, barren
deserts, or wide arms of the sea, capable of checking the free migration
of species from north to south. But notwithstanding the distinctness of
those zones of indigenous mammalia, there are some species, such as the
buffalo (_Bison Americanus_), the racoon (_Procyon lotor_), and the
Virginian opossum (_Didelphis Virginiana_), which have a wider
habitation, ranging almost from Canada to the Gulf of Mexico; but they
form exceptions to the general rule. The opossum of Texas (_Didelphis
carnivora_) is different from that of Virginia, and other species of the
same genus inhabit westward of the Rocky Mountains, in California, for
example, where almost all the mammalia differ from those of the United
States.

10thly. The _West Indian_ land quadrupeds are not numerous, but several
of them are pe