{23}Having already given a sketch, of the zoological features of the Neotropical region as a whole, the greater part of which will apply to this sub-region, we must here confine ourselves to an indication of the more important groups which, on the one hand, are confined to it, and on the other are absent; together with a notice of its special relations to other regions. _Mammalia._--Many of the most remarkable of the American monkeys are limited to this sub-region; as _Lagothrix_, _Pithecia_, and _Brachyurus_, limited to the great Amazonian forests; _Eriodes_ to south-east Brazil; and _Callithrix_ to tropical South America. All the marmosets (Hapalidæ) are also confined to this sub-region, one only being found at Panama, and perhaps extending a little beyond it. Among other peculiar forms, are 8 genera of bats; 3 peculiar forms of wild dog; _Pteronura_, a genus of otters; _Inia_, a peculiar form of dolphin inhabiting the upper waters of the Amazon; tapirs of the genus _Tapirus_ (a distinct genus being found north of Panama); 4 genera of Muridæ; _Ctenomys_, a genus of Octodontidæ; the whole family of Echimyidæ, or spiny rats, (as far as the American continent is concerned) consisting of 8 genera and 28 species; _Chætomys_, a genus of Cercolabidæ; the capybara (_Hydrochoerus_) the largest known rodent, belonging to the Caviidæ; the larger ant-eaters (_Myrmecophaga_); sloths of the genus _Bradypus_; 2 genera of armadillos (Dasypodidæ); and two peculiar forms of the opossum family (Didelphyidæ). No group that is typically Neotropical is absent from this sub-region, except such as are peculiar to other single sub-regions and which will be noticed accordingly. The occurrence of a solitary species of hare (_Lepus braziliensis_) in central Brazil and the Andes, is remarkable, as it is cut off from all its allies, the genus not being known to occur elsewhere on the continent further south than Costa Rica. The only important external relation indicated by the Mammalia of this sub-region is towards the Ethiopian region, 2 genera of Echimyidæ, _Aulacodes_ and _Petromys_, occurring in South and South-east Africa.