THE PLIOCENE. PERIOD. 327 
ford beds” as truly referable to this period, we meet at the 
close of this period with shells such as nowadays are distinct- 
ively characteristic of high latitudes. It might be thought 
that the occurrence of Quadrupeds such as the Elephant, 
Rhinoceros, and Hippopotamus, would militate against this 
generalisation, and would rather support the view that the 
climate of Europe and the United States must have been a 
hot one during the later portion of the Phocene period. We 
have, however, reason to believe that many of these extinct 
Mammals were more abundantly furnished with hair, and more 
adapted to withstand a cool temperature, than any of their 
living congeners. We have also to recollect that many of 
these large herbivorous quadrupeds may have been, and 
indeed probably were, more or less migratory in their habits ; 
and that whilst the winters of the later portion of the Pliocene 
period were cold, the summers might have been very hot. 
This would allow of a northward migration of such terrestrial 
animals during the summer-time, when there would be an 
ample supply of food and a suitably high temperature, and a 
southward recession towards the approach of winter. 
The chief palzontological interests of the Pliocene deposits, 
as of the succeeding Post-Pliocene, centre round the Mammals 
of the period ; and amongst the many forms of these we may 
restrict our attention to the orders of the Hoofed Quadrupeds 
(Ungulates), the Proboscideans, the Carnivora, and the Quad- 
vumana. Almost all the other Mammalian orders are more 
or less fully represented in Pliocene times, but none of them 
attains any special interest till we enter upon the Post-Pliocene. 
Amongst the Odd-toed Ungulates, in addition to the remains 
of true Tapirs (Zapirus Arvernensis), we meet with the bones 
of several species of Rhinoceros, of which the RAznoceros Etrius- 
cus and PR. megarhinus (fig. 249) are the most important. The 
former of these (fig. 249, A) derives its specific name from its 
abundance in the Pliocene deposits of the Val d’Arno, near 
Florence, and though principally Pliocene in its distribution, 
it survived into the earlier portion of the Post-Pliocene period. 
Rhinoceros Etruscus agreed with the existing African forms in 
having two horns placed one behind the other, the front one 
being the longest ; but it was comparatively slight and slender 
in its build, whilst the nostrils were separated by an incom- 
plete bony partition. In the RAznoceros megarhinus (fig. 249, 
B), on the other hand, no such partition exists between the 
nostrils, and the nasal bones are greatly developed in size. It 
was a two-horned form, and is found associated with Elephas 
meridionalis and £. antiguus in the Pliocene deposits of the 
