_I. South Temperate America, or the Chilian Sub-region._
This sub-region may be generally defined as the temperate portion of South America. On the south, it commences with the cold damp forests of Tierra del Fuego, and their continuation up the west coast to Chiloe and northward to near Santiago. To the east we have the barren plains of Patagonia, gradually changing towards the north into the more fertile, but still treeless, pampas of La Plata. Whether this sub-region should be continued across the Rio de la Plata into Uruguay and Entre-rios, is somewhat doubtful. To the west of the Parana it extends northward over the Chaco desert, till we approach the border of the great forests near St. Cruz de la Sierra. On the plateau of the Andes, however, it must be continued still further north, along the "paramos" or alpine pastures, till we reach 5° of South latitude. Beyond this the Andes are very narrow, having no double range with an intervening plateau; and although some of the peculiar forms of the temperate zone pass on to the equator or even beyond it, these are not sufficiently numerous to warrant our extending the sub-region to include them. Along with the high Andes it seems necessary to include the western strip of arid country, which is mostly peopled by forms derived from Chili and the south temperate regions.
_Mammalia._--This sub-region is well characterised by the possession of an entire family of mammalia having Neotropical affinities--the Chinchillidæ. It consists of 3 genera--_Chinchilla_ (2 sp.), inhabiting the Andes of Chili and Peru as far as 9° south latitude, and at from 8,000 to 12,000 feet altitude; _Lagidium_ (3 sp.), ranging over the Andes of Chili, Peru, and South Ecuador, { 37}from 11,000 to 16,000 feet altitude; and _Lagostomus_ (1 sp.), the "viscacha," confined to the pampas between the Uruguay and Rio Negro. Many important genera are also confined to this sub-region. _Auchenia_ (4 sp.), including the domesticated llamas and alpacas, the vicugna which inhabits the Andes of Peru and Chili, and the guanaco which ranges over the plains of Patagonia and Tierra del Fuego. Although this genus is allied to the Old World camels, it is a very distinct form, and its introduction from North America, where the family appear to have originated, may date back to a remote epoch. _Ursus ornatus_, the "spectacled bear" of the Chilian Andes, is a remarkable form, supposed to be most allied to the Malay bear, and probably forming a distinct genus, which has been named _Tremarctos_. Four genera of Octodontidæ are also peculiar to this sub-region, or almost so; _Habrocomus_ (1 sp.) is Chilian; _Spalacopus_ (2 sp.) is found in Chili and on the east side of the southern Andes; _Octodon_ (3 sp.) ranges from Chili into Peru and Bolivia; _Ctenomys_ (6 sp.) from the Straits of Magellan to Bolivia, with one species in South Brazil. _Dolichotis_, one of the Cavies, ranges from Patagonia to Mendoza, and on the east coast to 37½° S. latitude. _Myopotamus_ (1 sp.), the coypu (Echimyidæ), ranges from 33° to 48° S. latitude on the west side of the Andes, and from the frontiers of Peru to 42° S. on the east side. _Reithrodon_ and _Acodon_, genera of Muridæ, are also confined to Temperate South America; _Tolypeutes_ and _Chlamydophorus_, two genera of armadillos, the latter very peculiar in its organization and sometimes placed in a distinct family, are found only in La Plata and the highlands of Bolivia, and so belong to this sub-region. _Otaria_, one of the "eared seals" (Otariidæ), is confined to the coasts of this sub-region and the antarctic islands. Deer of American groups extend as far as Chiloe on the west, and the Straits of Magellan on the east coast. Mice of the South American genera _Hesperomys_ and _Reithrodon_, are abundant down to the Straits of Magellan and into Tierra del Fuego, Mr. Darwin having collected more than 20 distinct species. The following are the genera of Mammalia which have been observed on the shores of the Straits of Magellan, those marked * extending into Tierra del Fuego: { 38}*_Pseudalopex_ (two wolf-like foxes), _Felis_ (the puma), _Mephitis_ (skunks), _Cervus_ (deer), *_Auchenia_ (guanaco), *_Ctenomys_ (tucu-tucu), *_Reithrodon_ and *_Hesperomys_ (American mice).