history, we ascertain that the genus Didelphys was formerly found both in Europe and in North America during Eocene and Miocene times, so that it is possible that the Virginian

opossum may be a survivor rather than an intruder in North America.

The next order, the Edentates, is represented in this

Region only by a single species of armadillo (Tatusia novem-cincta), which almost certainly came up from the south, and is only met with just inside the southern borders.

Among the Ungulates, the most remarkable form is the prong-buck (Antilocapra), which forms a distinct family of that order, and is entirely confined to this Region (Fig. 30, p. 156). It is allied in some respects to the Antelopes of the

Old World, but it is unique among all the hollow-horned ruminants from the fact that it sheds its horns every year.

Two other genera, belonging to the family Bovidæ, are confined to the Nearctic Region; these are the Rocky Mountain goat (Haploceros), found only in the Rocky

Mountains (Fig. 31, p. 157); and the Musk Ox (Ovibos), which ranges over the barren grounds at the extreme north of the continent, and spreads into Greenland (see Fig. 32). The latter, however, was also found in the northern parts of the Old World until a comparatively recent epoch, geologically speaking.

The Bisons (Fig. 33) are still common to the Nearctic and Palearctic Region, though now nearly extinct in both hemispheres.

Rodents are very numerous in the Nearctic Region. According to the tables here used, which have been compiled from Flower and Lydekker's text-book of

mammals, out of a total number of twenty-eight genera, thirteen are endemic. One of these, Haplodon, a small animal resembling the Prairie-dog in its habits, and found only west of the Rocky Mountains, forms a distinct family. The Carnivora are also well represented, especially the genera of Cats, Dogs, Bears, and Weasels, all of which,

however, are widely spread. The only endemic genus is that formed for the reception of the American Badger (Taxidea), which differs from its European ally in certain anatomical features.

In contradistinction to the Neotropical Region, the Insectivora are abundant in the Nearctic; there are no less

than four genera of Moles met with, three of which are peculiar.

Amongst them is the remarkable Star-nosed Mole (Condylura cristata) which carries a ring of riband-like appendages at the end of its snout. These serve, no doubt, as a sensitive organ (see Fig. 34).

Finally, the Bats are neither very numerous nor of