CHAP. VII. ] MAMMALIA OF THE NEW WORLD. 141 
to ascertain their relations to each other, and to see how far 
they elucidate the problem of the birth-place and subsequent 
migrations of the several families and genera. We have already 
pointed out the remarkable features of the Quaternary (or Post- 
Pliocene) fauna of North America, and now proceed to discuss 
that of the various Tertiary periods, which is closely connected 
with the extinct fauna of Europe. 
The Tertiary Mammalia of North America at present de- 
scribed belong to from eighty to one hundred genera, while 
those of Europe are nearly double that number; yet only 
eighteen genera are common to the two faunas, and of these 
eight are living and belong chiefly to the Pliocene period. 
Taking first, the genera which in America do not go back beyond 
the Pliocene period (ten in number), we find that eight of them 
in Europe go back to the Upper Miocene. These are Felis, 
Pseudelurus, Hipparion, Cervus, Mastodon, Elephas (in India), 
Castor and Hystriz; while another, Canis, goes back to the 
Upper Eocene and the tenth, Hquwus, confined to the newer 
Pliocene or perhaps to the Post-Pliocene in America, extends 
back to the older Pliocene in Europe. Of the seven European 
genera which are confined to the Miocene period in America, 
three, Hycenodon, Anchitherium, and Lophiodon go back to the 
Eocene in Europe; three others, Machairodus, Rhinoceros, and 
Acevatherium, are also of Miocene age in Europe; Amphicyon goes 
back to the Lower Miocene of Europe. Lophiotherium belongs 
to the Eocene of both countries. 
If we turn now to families instead of genera, we find that the 
same general rule prevails. Mustelidz (weasels), Urside (bears), 
true Equide (horses), and Bovide (oxen &c.), go no further back 
in America than the Pliocene, while they all go back to the 
Miocene in Europe. Suidz (swine) and Anoplotheride (extinct) 
are found in the American Miocene and in the European Eocene. 
Anchitheridz (extinct) reach the Upper Eocene in America, 
while in Europe they range through Upper, Middle, and Lower 
Eocene. Cervidee (deer) alone are Miocene in both countries. 
There remain two families in which America has the pre- 
eminence. Camelidz (camels) were wonderfully developed in 
