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62 ZOOLOGICAL GEOGRAPHY. [part hi.
soil of a large portion of it is very fertile, it is altogether well
adapted to support a varied fauna, as it does a most luxuriant
vegetation. Although many peculiar Neotropical types are
absent, it yet possesses an ample supply of generic and specific
forms ; and, as far as concerns birds and insects, is not perhaps
inferior to the richest portions of South America in the number
of species to be found in equal areas.
Owing to the fact that the former Republic of Mexico
comprised much territory that belongs to the Nearctic region,
and that many Nearctic groups extend along the high-lands to
the capital city of Mexico itself, and even considerably further
south, there is much difficulty in determining what animals
really belong to this sub-region. On the low-lands, tropical
forms predominate as far as 28° N. latitude ; while on the
Cordilleras, temperate forms prevail down to 20°, and are found
even much farther within the tropics.
Mammalia.—Very few peculiar forms of Mammalia are re-
stricted to tropical North America ; which is not to be wondered at
when we consider the small extent of the country, and the facility
of communication with adjacent sub-regions. A peculiar form
of tapir {Elasmognathus hairdi) inhabits Central America, from
Panama to Guatemala, and, with Myxomys, a genus of Muridse,
are all at present discovered. Bassaris, a remarkable form of
Procyonidee, has been included in the Nearctic region, but it
extends to the high-lands of Guatemala. Heteromys, a peculiar
genus of Saccomyidse or pouched rats, inhabits Mexico,
Honduras, Costa Eica, and Trinidad. Five genera of monkeys
extend here, Ateles, Mycetes, Cehus, Nydipithecus, and Saimiris ;
the two former alone reaching Mexico, the last only going as far
as Costa Eica. Other typical Neotropical forms are Galera, the
tayra, belonging to the weasel family ; Kasita, the coatimundi
Dicotyles, the peccary ; Cercolahes, the tree porcupine ; Dasyprocta,
the agouti ; Cmlogenys, the paca ; Chulcepus, and Arctopithecus,
sloths ; Cydothurus, an ant-eater ; Tatusia, an armadillo ; and
Didelphys, oppossum. Of Northern forms. Sorex, Vulpes, Lepus,
and Pteromys reach Guatemala.
Birds.—The productiveness of this district in bird life, may