MAMMALIA. 103 
On the other hand, there are a great many genera like the Prongbuck (Antzlocapra), 
Bison (formerly), Rocky Mountain Sheep, Beaver, Prairie-Marmot (Cynomys), Chipmunk 
(Lutamias), Black Bear, Wolf, Lynx, and other typically North American forms which 
are restricted in Central America to the Mexican plateau or to the highlands just to 
the south of it. 
These differences in distribution exist quite apart from the occurrence throughout 
Central America of many families and genera like the Hares (Leporide), the typical 
Squirrels (Sczwrus etc.), the Shrews (Soricide), Pocket Gophers (Geomyide), Raccoon 
(Procyon), Deer (Odocoileus), and others. 
Zoogeographers have given practical expression to the facts above set forth by 
referring the plateau of Mexico to the same zoological region as the southern States of 
North America. Out of a number of titles that have been proposed for this region, 
Sonoran is the one preferred. The rest of Central America, on the other hand, is 
regarded as a subregion of the Neotropical Region—sometimes called the Neogzic 
Realm,—which embraces, in addition, the Antilles and the whole of South America. 
On the western side of the plateau this region stretches to about lat. 25° N., and on 
the eastern side a little farther, stopping short near the Nueces River in Texas. 
The subregional distinctions between the tropical portions of Central America and the 
adjacent portions of South America are not sharply defined, and rest upon the not very 
satisfactorily established statistics of the comparatively small number of typically 
South American genera which occur in those areas of Central America, and the 
presence in the latter of certain Sonoran forms (Soricide, Geomyide) whose southward 
range practically stops short at Panama. 
Similarly, the Antillean subregion is characterised mainly by the poverty of its fauna 
in types occurring in Central and South America, It is noticeable that the orders of 
known northern origin are practically absent. Some of the Chiroptera (Eptesicus, 
Myotis) are, perhaps not surprisingly, exceptional. Most of the genera of this order 
belong to the Tropical American family Phyllostomide. For the rest, the Hystrico- 
morph Redents are represented by Capromys, Plagiodontia, and Loncheres, all Octodonts, 
the first two being peculiar to the subregion, by Dasyprocta, and possibly by a species 
of Coendow. Very interesting is the occurrence of a Cricetine Myomorph, Megalomys, 
peculiar to the Lesser Antilles. Monkeys, however, are absent, and the Edentates are 
represented only by one species of Armadillo (Dasypus) from Grenada. Finally, the 
Insectivora are exemplified by the Cuban and Haitian Solenodon, whose nearest living 
allies are the Centetide of Madagascar (Centetes etc.) and West Africa (Potamogale). 
The family Solenodontide, however, dates back to the Lower Oligocene in North 
America, where one genus, MZicropternodus, has been discovered. 
Until the Mammalian Paleontology of the West Indies has been worked out, the 
geological history of these islands cannot be accurately read. Nevertheless, temporary 
union between the Lesser Antilles and South America is indicated by the occurrence 
