l is shorter than the body, moderately
bushy, narrow at the base, but expanding towards the tip; the hairs
are broadly banded with four alternate pale and dark brown bands,
the last being the darkest and broadest, with a pale tip; the
under-parts are white in some, rich orange yellow in others.

SIZE.--Head and body, 7-1/2 inches; tail reaches to the eye.

* * * * *

The Flying Squirrels next engage our attention. In several groups
of animals of strictly arboreal habits, nature has gone beyond the
ordinary limits of agility afforded by muscular limbs alone, and has
supplemented those limbs with elastic membranes which act like a
parachute when the animal takes a leap into space, and gives it a
gradual and easy descent. Amongst the lemurs the _Galeopithecus_,
the _Pteromys_ in the squirrels, and the _Anomalurus_ in another
family of rodents, are all thus provided with the apparatus necessary
to enable them to float awhile in the air, for flying is scarcely
the proper term for the letting-down easy principle of the mechanism
in question.

The flying squirrels, with which we have now to deal, are in general
details the same as ordinary squirrels, but the skin of the flanks
is extended between the fore and hind limbs, which, when spread out,
stretches it into a wide parachute, increased in front by means of
a bony spur which projects from the wrist. These animals have been
subdivided into the large round-tailed flying squirrels, _Pteromys_,
and the small flat-tailed flying squirrels, _Sciuropterus_. The
distinction was primarily made by F. Cuvier on the character of the
teeth, as he considered _Sciuropterus_ to have a less complex system
of folds in the enamel of the molars, more like the ordinary squirrels
than _Pteromys_; but modern research has proved that this is not a
good ground for distinction. Dr. Anderson has lately examined the
dentition in eleven species of _Pteromys_ and _Sciuropterus_, and
he says: "According to my observations the form of the enamel folds
in youth are essentially similar, consisting of a series of
tubercular folds which are marked with wavy lines in some, and are
smooth in others, but in all there is a marked conformity to a common
type. The seemingly more complex character of the folds appears to
depend on the extent to which the tubercular ridges are worn by use."
He also questions the propriety of the separation according to the
distichous arrangement of