Page:A History of Land Mammals in the Western Hemisphere.djvu/195

Rh, detached at a comparatively recent date; the southern extremity of Florida also belongs to this subregion.

The two subregions into which continental South America is divided are not altogether satisfactory and will doubtless require change when the distribution of South American mammals has been more accurately determined.



"Richness combined with isolation is the predominant feature of Neotropical Zoölogy, and no other region can approach it in the number of its peculiar family and generic types" (Wallace). Just as North America has received many immigrants from the Old World, so it has sent many migrants into South America, materially changing the character of the Neotropical mammalian fauna, but these intruders may be readily identified and almost seem to be out of place in their new surroundings. Not all of these northern migrants were