132 DISTRIBUTION OF EXTINCT ANIMALS, [PART II. 
migration had occurred for countless preceding ages, proves that 
some great barrier to the entrance of terrestrial mammalia 
which had previously existed, must for a time have been re- 
moved. We must defer further discussion of this subject till 
we have examined the relations of the existing faunas of North 
and South America. 
TERTIARY PERIOD. 
When we get to remains of the Tertiary age, especially those 
of the Miocene and Eocene epochs, we meet with so many 
interesting and connected types, and such curious relations with 
living forms in Europe, that it will be clearer to trace the 
history of each order and family throughout the Tertiary period, 
instead of considering each of the subdivisions of that period 
separately. 
It will be well however first to note the few American Post- 
Pliocene or living genera that are found in the Pliocene beds. 
These consist of several species of Cans, from the size of a fox 
to that of a large wolf; a Felis as large as a tiger; an Otter 
(Lutra); several species of Hipparion; a peccary (Dicotyles) ; 
a deer (Cervus) ; several species of Procamelus ; a mastodon ; 
an elephant; and a beaver (Castor). It thus appears that out 
of nearly forty genera found in the Post-Pliocene deposits, only 
ten are found in the preceding Pliocene period. About twelve 
additional genera, however, appear there, as we shall see in 
going over the various orders. 
Primates—Among the vast number of extinct mammalia 
discovered in the Tertiary deposits of North America, no 
example of this order had been recognized up to 1872, when 
the discovery of more perfect remains showed, that a number 
of small animals of obscure affinities from the Lower Eocene 
of Wyoming, were really allied to the lemurs and perhaps 
also to the marmosets, the lowest form of American monkeys, 
but having a larger number of teeth than either. A number of 
other remains of small animals from the same formation, pre- 
viously supposed to be allied to the Ungulata, are now shown to 
