_Neotropical Region._—The last of the six main regions is the Neotropical, including Mexico, South America, and the West Indies. A very large extent of this area is occupied by forests, which are described as being denser and more luxuriant than those of any other part of the globe. Alternating with these forest areas are the vast grassy plains known in different regions as llanos, savannas, and pampas. The back-bone of the region is formed by the great chain of the Andes. Next to the Australasian, this region is perhaps better characterised by its mammalian fauna than any of the others. Commencing with the Ungulates, we find a total absence of Antelopes, Sheep, and Oxen, and also of all Perissodactyles except Tapirs. Deer are, however, represented, although by peculiar forms (_Cariacus_) unknown beyond the New World. The Peccaries (_Dicotyles_), which are often made the type of a distinct family, take the place of the Old World Pigs, while the Llamas and Alpacas (_Auchenia_) are the substitutes for the Palæarctic Camels. The Carnivora include several Cats (_Felis_), among which the Puma and the Jaguar are the most noticeable; and there are also Raccoons, Coatis, Foxes, and one species of Bear. Insectivora are totally wanting; but the Bats are characterised by the presence of the Vampyres (_Phyllostomatidæ_), which are almost restricted to this region. The Rodents likewise include three families unknown elsewhere, namely the Chinchillas and Viscacha (_Chinchillidæ_), the Agouties (_Dasyproctidæ_), and the Cavies (_Caviidæ_); while a large number of the _Octodontidæ_ are Neotropical, all the other forms being Ethiopian. In the Primates, again, we have all the forms quite peculiar to this region, and constituting two families, viz. the _Cebidæ_ or Prehensile-tailed Monkeys, and the _Hapalidæ_, or Marmosets, both of which differ decidedly in their dentition, as well as in other features, from the Old World Monkeys. Lemuroids are unknown. Perhaps, however, the mammals which may be considered as most characteristic of the Nearctic region are the numerous Edentates, which form three families, mostly confined to it. These comprise the _Bradypodidæ_ or Sloths, which solely inhabit the forest region; the _Myrmecophagidæ_ or Anteaters; and the _Dasypodidæ_ or Armadillos, of which one species has crept northward as far as Texas. Almost equally characteristic are the numerous Opossums, the majority of which belong to the genus _Didelphys_. Finally, it should be observed that the West Indies are distinguished from the rest of the region by the absence of Primates, Carnivora, and Edentates.