North America four quite distinct types can be made out. First of these
is the circumpolar species, _Ursus maritimus_, the white or polar
bear, which most of us grew up to regard as the very incarnation of
tenacious ferocity, but which, as it appears from the recitals of
late Arctic explorers, dies easily to a single shot, and does not
seem to afford much better sport than so much rabbit shooting.
The others are the great Kadiak bear (_U. middendorfi_); the
grizzly (_U. horribilis_), and the black or true American bear
(_U. americanus_). The extent to which the last three may
be subdivided remains uncertain, but the barren-ground bear
(_U. richardsoni_) is surely a valid species of the grizzly type.
The grizzlies and the big Alaska bears approach more nearly than
_americanus_ to the widespread brown bear (_U. arctos_) of
Europe and Asia, and the hypothesis is reasonable that they originated
from that form or its immediate ancestors, in which case we have the
interesting series of parallel modifications exhibited in the two
continents, for the large bear of Kamtschatka approaches very nearly to
those of Alaska, while further to the south in America, where the
conditions of life more nearly resemble those surrounding _arctos_,
these bears have in the grizzlies retained more of their original form.
Whether or not the large Pleistocene cave bear (_U. spelaeus_) was a
lineal ancestor is questionable, for in its later period, at least, it was
contemporary with the existing European species. The black bear, with its
litter-brother of brown color, seems to be a genuine product of the new
world.

Many differential characters have been pointed out in the skulls and teeth
of bears, and to a less extent, in the claws; but while these undoubtedly
exist, the conclusions to be drawn from them are uncertain, for the
skulls of bears change greatly with age, and the constancy of these