ON THE EXTINCT ANIMALS OF NORTH AMERICA. 
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attributed to the Eocene epoch have been obtained ; although 
still more recently fossiliferous beds of the same age have been 
discovered both in Colorado and New Mexico, so rich as to give 
hopes that we are still only on the threshold of our knowledge 
of the wonderful fauna of the ancient American continent. 
Besides the extensive and older known Miocene and Pliocene 
beds between the Rocky Mountains and the Missouri, others of 
corresponding age have been discovered west of the Blue 
Mountains in Eastern Oregon. 
I must now pass in successive review some of the principal 
groups into which animals have been divided by naturalists, and 
show what is known of their past history on the great North 
American continent. I am aware that the summary I am about 
to give will be exceedingly imperfect, partly on account of the 
limited time allowed in one discourse, and partly on account of 
the difficulty of extracting a connected account of these 
discoveries from the exceedingly numerous notices in which 
they are described — often fragmentary and disconnected, and 
even contradictory, and scattered through a variety of periodicals 
and reports. As most of these descriptions are put forth by 
their authors as “ preliminary,” to be superseded by more 
elaborate and detailed work hereafter, so must this notice of 
them be regarded. It will at least serve the purpose of calling 
attention to the importance and interest of this comparatively 
new field of research. 
The first group to which I will direct attention, as it is 
that of the ancient history of which we have more complete 
knowledge than of any other, is the large order of Ungulata , 
or hoofed animals ; and first among them I will consider those 
characterised, among many other distinctive peculiarities, by 
the uneven or jperissodactyle structure of the foot, represented 
in the actual fauna of the world only by the three families of 
Horses, Tapirs, and Rhinoceroses — animals differing very con- 
siderably from each other in general outward appearance, and 
yet having many important common characteristics. 
It is well known that in the Old World, species of this group, 
very intermediate in characters to those now existing, flourished 
in the Eocene age. Cuvier’s grand researches in the Paris 
gypsum beds, which laid the foundation of the study of mam- 
malian paleontology, reconstructed the form, now almost as 
well known as that of the existing tapir, of the Palceotherium ; 
and numerous allied species have since been found, not only in 
France, Switzerland, and Germany, but in the corresponding 
beds in our own country. But in America, before 1869, not a 
single Eocene Perissodactyle had been discovered. In fact, as 
just mentioned, no Eocene beds containing the remains of 
terrestrial animals had been explored. Since that date, how- 
