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Show i9oo] ANIMAL LIFE 57 y continent, and is subdivided into cold temperate and warm temperate sub - regions, the line of division being the isotherm of 430 F., or, roughly speaking, the boundary- line between Canada and the United States. \ South of the North American temperate region is the American tropical realm, including Central America, the West Indies, and a part of Mexico, Florida, and Lower California. Proceeding to k surVey of the fauna of North America, and takingv* lflrst the American arctic region^ the area beyond the tree limit, we find that it has no specific fauna. \ Its animal inhabitants are all circumpolar in distribution, and occur also in arctic Eurasia. The most notable arctic animals are the polar bear, arctic fox, arctic hare, the musk-ox ( now extinct in the Old World), the white lemming, barren- ground caribou, the walrus, and, among birds, the willow ptarmigan. The seals are abundant, but certain species found in the eastern ( Barren Ground) and western ( Alaskan) groups are not identical. vPassing to the north temperate realm we find a sharp distinction from the fauna of the arctic region. 1 The total number of genera of land mammals in the two regions is one hundred and forty, of which ninety - seven occur in Eurasia and seventy - five in North America. Of these, thirty- two are circumpolar, or common to both 1 Allen, Geographical Distribution of North American Animals, 210. |
