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Show 58 BASIS OP AMERICAN HISTORY [ 1500 regions; and out of the seventy - five in America only twenty - seven, a trifle over one - third, are peculiarly American. The most interesting result, however, appears in the comparison of the % corresponding sub- regions of the two continents. Of forty- three genera in the North American cold temperate sub- region, six are common to both cold and warm, and seventeen are limited to the warm sub- region. 1 The general result, then, of the faunal comparison of the two continents is that the arctic faunas exhibit no difference, the north temperate sub- regions very little, and that specific differentiation increases rapidly as we pass southward. It may be well to recall that the comparison deals with genera; t; he great majority of species in both continents are of course peculiar. The North American tropical region has sixty-two genera of mammals, and the fauna is widely divergent from that of the tropical regions of the Old World. The most characteristic mammals are the ant- eater, armadillo, sloth, tapir, peccary, jaguar, marmoset, and spider- monkey. Proceeding to a consideration of the animals themselves in their relations to man, we shall notice such animals as are of economic importance, as sources of food, clothing, or other necessities; and the group which pre- eminently serves these functions is the ruminants. Of these the family which, all things 1 It is an interesting fact that the majority of these peculiarly American genera are rodents. |