untry. Add to these such peculiar birds as the mocking thrushes (Mimus),
the blue jays (Cyanocitta), the tanagers, the peculiar genera of cuckoos
(Coccygus and Crotophaga), the humming-birds, the wild turkeys (Meleagris),
and the turkey-buzzards (Cathartes), and we see that if there is any doubt
as to the mammals of North America being sufficiently distinct to justify
the creation of a separate region, the evidence of the birds would alone
settle the question.

The reptiles, and some others of the lower animals, add still more to this
weight of evidence. The true rattlesnakes are highly characteristic, and
among the lizards are several genera of the peculiar American family, the
Iguanidae. Nowhere in the world are the tailed batrachians so largely
developed as in this region, the Sirens and the Amphiumidae forming two
peculiar families, while there are nine peculiar genera of salamanders, and
two others allied respectively to the Proteus of Europe and the Sieboldia
or giant salamander of Japan. There are seven peculiar families and about
thirty peculiar genera of fresh-water fishes; while the fresh-water
molluscs are more numerous than in any other region, more than thirteen
hundred species and varieties having been described.

Combining the evidence derived from all these classes of animals, we find
the Nearctic region to be exceedingly well characterised, and to be amply
distinct from the Palaearctic. The few species that are common to the two
are almost all arctic, or, at least, northern types, and may be compared
with those desert forms which occupy the debatable ground between the
Palaearctic, Ethiopian, and Oriental regions. {51} If, however, we compare
the number of species, which are common to the Nearctic and Palaearctic
regions with the number common to the western and eastern extremities of
the latter region, we shall find a wonderful difference between the two
cases; and if we further call to mind the number of important groups
characteristic of the one region but absent from the other, we shall be
obliged to admit that the relation that undoubtedly exists between the
faunas of North America and Europe is of a very distinct nature from that
which connects together Western Europe and North-eastern Asia in the bonds
of zoological unity.

_Definition and Characteristic Groups of the Neotropical Region._--The
Neotropical region requires very little definition, since it comprises the
whole of America south of th