GEOGRAPHICAL ZOOLOGY. 
[part IV. 
2:36 
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. Spermophilus goes back to the Upper 
Miocene ; Arctomys 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 Sciumvus, 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.— HAPLOODONTHUE,— (1 Genus, 2 Species.) 
General Distribution. 
Neotropical 
SirB-REGIONS. 
Nearctic 
Sub-regions. 
Pal^earctic 
Sub-regions. 
Ethiopian | 
Sub-regions. 
Oriental 
Sub-regioNs. 
Australian 
Sub-regions. 
The genus Haploodon or Aplodontia , consists of two curious 
rat-like animals, inhabiting the west coast of America, from the 
southern part of British Columbia to the mountains of Califor- 
nia. They seem to have affinities both with the beavers and 
marmots, and Professor Lilljeborg constitutes a sepai ate family 
to receive them. 
