52 
ZOOLOGICAL GEOGRAPHY. 
[part III. 
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 Eepublic 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 (Elasmognatlms bairdi) inhabits Central America, from 
Panama to Guatemala, and, with Myxomys , a genus of Muridae, 
are all at present discovered. Bassaris, a remarkable form of 
Procyonidse, 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, Cebus, Nyciipithecus , 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 ; Mama, the coatimundi ; 
Dicotyles, the peccary ; Gercolabes , the tree porcupine ; Dasyproda , 
the agouti ; Coelogenys, the paca ; Cholcepus , and Ardopithems, 
sloths; Cyclothurus, an ant-eater; Tatusia , an armadillo; and 
D'idelphys, oppossum. Of Northern forms, Sorex, Vulp&s, Zepus , 
and Pteromys reach Guatemala. 
Birds. — The productiveness of this district in bird life, may 
