to the plains of temperate South
America.

_General features of Overlapping and Discontinuous Areas._--These numerous
examples of discontinuous genera and families form an important section of
the facts of animal dispersal which any true theory must satisfactorily
account for. In greater or less prominence they are to be found all over
the world, and in every group of animals, and they grade imperceptibly into
those cases of conterminous and overlapping areas which we have seen to
{29} prevail in most extensive groups of species, and which are perhaps
even more common in those large families which consist of many closely
allied genera. A sufficient proof of the overlapping of generic areas is
the occurrence of a number of genera of the same family together. Thus in
France or Italy about twenty genera of warblers (Sylviadae) are found, and
as each of the thirty-three genera of this family inhabiting temperate
Europe and Asia has a different area, a great number must here overlap. So,
in most parts of Africa, at least ten or twelve genera of antelopes may be
found, and in South America a large proportion of the genera of monkeys of
the family Cebidae occur in many districts; and still more is this the case
with the larger bird families, such as the tanagers, the tyrant shrikes, or
the tree-creepers, so that there is in all these extensive families no
genus whose area does not overlap that of many others. Then among the
moderately extensive families we find a few instances of one or two genera
isolated from the rest, as the spectacled bear, Tremarctos, found only in
Chili, while the remainder of the family extends from Europe and Asia over
North America to the Mountains of Mexico, but no further south; the
Bovidae, or hollow-horned ruminants, which have a few isolated genera in
the Rocky Mountains and the islands of Sumatra and Celebes; and from these
we pass on to the cases of wide separation already given.

_Restricted Areas of Families._--As families sometimes consist of single
genera and even single species, they often present examples of very
restricted range; but what is perhaps more interesting are those cases in
which a family contains numerous species and sometimes even several genera,
and yet is confined to a narrow area. Such are the golden moles
(Chrysochloridae) consisting of two genera and three species, confined to
extratropical South Africa; the hill-tits (Liotrichidae), a family of
numerous genera and spec