ed on
one side by their crowns; and it is this peculiarity which is
expressed by the generic name (Gr. _zeugle_, a yoke; _odous_,
tooth). The best-known species of the genus is the _Zeuglodon
cetoides_ of Owen, which attained a length of seventy feet. Remains
of these gigantic Whales are very common in the "Jackson Beds" of
the Southern United States. So common are they that, according
to Dana, "the large vertebrae, some of them a foot and a half
long and a foot in diameter, were formerly so abundant over the
country, in Alabama, that they were used for making walls, or
were burned to rid the fields of them."

[Illustration: Fig. 228.--_Zeuglodon cetoides_. A, Molar tooth of
the natural size; B, Vertebra, reduced in size. From the Middle
Eocene of the United States. (After Lyell.)]

The great and important order of the Hoofed Quadrupeds (_Ungulata_)
is represented in the Eocene by examples of both of its two principal
sections--namely, those with an uneven number of toes (one or three)
on the foot (_Perissodactyle Ungulates_), and those with an even
number of toes (two or four) to each foot (_Artiodactyle Ungulates_).
Amongst the Odd-toed Ungulates, the living family of the Tapirs
(_Tapirdoe_) is represented by the genus _Coryphodon_ of Owen.
Nearly related to the preceding are the species of _Paloeotherium_,
which have a historical interest as being amongst the first of
the Tertiary Mammals investigated by the illustrious Cuvier.
Several species of _Paloeothere_ are known, varying greatly in
size, the smallest being little bigger than a hare, whilst the
largest must have equalled a good-sized horse in its dimensions. The
species of _Paloeotherium_ appear to have agreed with the existing
Tapirs in possessing a lengthened and flexible nose, which formed
a short proboscis or trunk (fig. 229), suitable as an instrument
for stripping off the foliage of trees--the characters of the
molar teeth showing them to have been strictly herbivorous in
their habits. They differ, however, from the Tapirs, amongst
other characters, in the fact that both the fore and the hind
feet possessed three toes each; whereas in the latter there are
four toes on each fore-foot, and the hind-feet alone are three-toed.
The remains of _Paloeotheria_ have been found in such abundance in
certain localities as to show that these animals roamed in great
herds over the fertile plains of France and the south of England
during the later portion of the Eo