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236 GEOGRAPHICAL ZOOLOGY. [part iv.
Extinct Sciuridce.—These are tolerably abundant. The genus
Sciurus appears to be a remarkably ancient form, extinct species
being found in the Miocene, and even in the Upper Eocene
formations of Europe. Sjpermophilus goes back to the Upper
Miocene ; Ardomys to the Newer Pliocene. Extinct genera are,
Brachymys, Lithomys and Plesiarctomys, from the European
Miocene, the latter said to be intermediate between marmots
and squirrels.
In North America, Sciurus, Tamias, and Arctomys occur in the
Post-pliocene deposits only. The extinct genera are Ischyromys,
from the Upper Miocene of Nebraska ; Paramys, allied to the
marmots, and Sciuravus, near the squirrels, from the Eocene of
Wyoming.
Here we have unmistakable evidence that the true squirrels
(Sciurus) are an Old World type, which has"only recently entered
North America ; and this is in accordance with the comparative
scarcity of this group in South America, a country so well
adapted to them, and their great abundance in the Oriental
region, which, with the Palsearctic, was probably the coun-
try of their origin and early development. The family, how-
ever, has been traced equally far back in Europe and North
America, so that we have as yet no means of determining where
it originated.
Family 62.—HAPLOODONTID^.—(1 Genus, 2 Species.)
General Distribution.