140 DISTRIBUTION OF EXTINCT ANIMALS. [PART II. 
seven species allied to Tillotherium and Anchippodus, and having 
also relations, as Professor Cope believes, with the South American 
Toxodontide. 
Rodentia—This order is represented in the Pliocene by a 
beaver, a porcupine, and an American mouse (Hesperomys), all 
extinct species of living genera, the Hystriz being an Old World 
type; and Professor Cope has recently described Panolax, a 
new genus of hares from the Pliocene of New Mexico. The 
Miocene deposits have furnished an extinct genus allied to the 
hares—Paleolagus; one of the squirrel family—Ischyromys ; 
a small extinct form of beaver—Palwocastor ; and an extinct 
mouse—Humys. The Eocene strata of Wyoming have lately 
furnished two extinct forms of squirrel, Paramys and Sciwravus ; 
and another of the Muridz (or mouse family), J/ysops. 
Cetacea—Numerous remains of dolphins and whales, be- 
longing to no less than twelve genera, mostly extinct, have been 
found in the Miocene deposits of the Atlantic and Gulf States, 
from New Jersey to South Carolina and Louisiana; while seven 
genera of the extinct family, Zeuglodontide, have been found in 
Miocene and Eocene beds of the same districts. Some remains 
associated with these are doubtfully referred to the Seal family 
(Phocidz) among the Carnivora. 
Edentata—Till quite recently no remains of this order have 
occurred in any North American deposits below the Post-Plio- 
cene; but in 1874 Prof. Marsh described some remains allied to 
Megalonyx and Mylodon, from the Pliocene beds of California 
and Idaho, and forming a new genus, Morotherium. As these 
remains have only occurred to the west of the Rocky Mountains, 
and in Pliocene deposits whose exact age is not ascertained, they 
hardly affect the remarkable absence of this group from the 
whole of the exceedingly rich Tertiary deposits in all other parts 
of North America. 
General Relations of the extinct Tertiary Mammalia of North 
America and Europe—Having now given a sketch of the ex- 
tinct Mammalia which inhabited Europe and North America 
during the Tertiary period, we are enabled by comparing them, 
