FLYING SQUIRRELS. 89 
excavation, the woodchuck will sometimes take up its abode in rocky ledges or in 
the hollow roots of trees. During the summer the greater number of these animals 
live in the open fields; but in the winter it appears that in the Adirondack region 
at least they retire for the winter to burrows situated close to, or actually within, 
the borders of woods. In the Adirondacks the woodchucks become very fat in the 
early autumn, and retire for their winter sleep—no matter what be the temperature 
or the state of the weather—about the equinox, from which they do not awake 
till the middle or latter part of March. Still more remarkable is the circumstance 
that the animal often retires when the weather is genial and food abundant, while 
at the time of its reappearance the ground is frequently deep in snow. 
“Woodchucks,” writes Dr. Merriam, “are both nocturnal and diurnal, the 
periods of feeding being determined, in a general way, by the time of the year, the 
weather, and the proximity of enemies. In summer, throughout the farming 
districts, they commonly leave their burrows early in the morning, late in the 
afternoon, and during moonlight nights; but may sometimes be found abroad at 
all hours. As autumn approaches, and they become more fat and sleepy, they 
usually appear only in fine weather, and then but for a few hours in the hottest 
part of the afternoon.” Like the Old World species, the woodechuck when much 
hunted becomes exceedingly wary and difficult to approach; but it differs from all 
the latter in that it will sometimes ascend trees and shrubs—making these ascents 
sometimes for pleasure and at others to avoid foes. _Woodchucks live either singly 
or in pairs; the young, which are born at the end of April or beginning of May in 
the Adirondack district, remaining with their parents only a few months. The 
number in a litter is usually from four to six. When the young first leave their 
parents they take refuge in stone walls, hollow logs, or even hollow trees—habits 
quite different from those of their Old World cousins, and showing a marked 
approximation towards the chipmunks. 
In some parts of New Hampshire woodchucks are so numerous as to cause 
serious inconvenience to agriculturists, and rewards have consequently been offered 
by the State for their destruction. 
Extinct Marmot- Remains of extinct species of susliks occur in the higher 
like Rodents. Tertiary rocks of Europe; in addition to which the Upper Eocene 
beds of France yield evidence of an extinct but apparently allied genus, known as 
Plesispermophilus. More primitive are the forms described as Plesiarctomys, 
which, while showing certain resemblances both to the marmots and the squirrels, 
have triangular three-cusped upper molar teeth, and no bony process defining the 
hinder limit of the upper border of the socket of the eye. These Rodents are 
found in the Middle Tertiary deposits both of Europe and North America. 
THE FLYING SQUIRRELS. 
Genera Sciwropterus, Pteromys, and Eupetawrus. 
The flying squirrels of the Northern Hemisphere, which are divided into the 
three generic groups named above, are sufficiently characterised by possessing a 
parachute-like membrane extending from the sides of the body to the toes, and 
