368° O. C. Marsh— Vertebrate Life in America 
Eocene. The earliest ere forms are apparently all related 
to the Squirrels, and the most common genus is Scturavus, 
which continued pamiaen the Kocene. A nearly allied form, 
which may prove to be the same, is Paramys, the Fee: of 
which are larger than those of the older type. the Dino- 
ceras beds, the genus Colonomys is found, and the specimens 
preserved point to the J/uride, as the nearest living allies. A 
peculiar genus, Apatemys, which also occurs in the middle 
Eocene, has gliriform incisors, but the molars resemble those of 
Insecti vores, All the Kocene Rodents are of small size, the 
largest being about as large as a rabbit. 
In the middle and upper Miocene lake-basins of the West, 
Rodents abound, but all are of moderate size. The Hares first 
appear in the Oreodon see and continue in considerable num- 
bers through the rest of the Tertiary and Post-Tertiary to the 
present day. In these beds, the most common forms belong to 
the Leporide, and mainly to the genus Paleolagus. The Squirrel 
family is represented by Ischyromys, the Muride by the genus 
Fumys, and the Beavers by Paleocastor. In the upper Miocene 
of Oregon, most of ia same genera are found, and with them 
some peculiar forms, very unlike anything now living. One o 
these is the genus Allomys, possibly related to the flying 
Squirrels, but having molar teeth somewhat like those of the 
Ungulates. In the Pliocene, east and west of the Rocky Moun- 
tains, Rodents continue abundant, but most of them belong to 
existing genera. Among these are Castor, Hystrix, Cynomys, 
Geomys, Lepus and Lesperomys. In the Post-Tertiary, the 
gigantic beaver, Castoroides, was abundant throughout most of 
orth America. Hydrocherus has been found in South Caro- 
lina. In the caves of the island of Anguilla, in the West 
Indies, remains of large extinct Rodents belonging to the Chin- 
chillide have been discovered. 
The early Tertiary Rodents known from South America are 
the genera ae, pits aad and a large species referred 
to Arvicola. In Brazil, the Pliocene Rodents found are referred 
to the existing g pie Cavia, Kerodon, Lagostomus, Ctenomys, 
Hesperomys, Oxymycter us, Arvicola ana ‘Lepus. A new genus, 
Cardiodus, described from this horizon, is a true Rodent, but 
the peculiar Zypotherium, which has been referred to this order 
some authorities, has perhaps other affinities. In the 
Post-Tertiary, the Rodents were very abundant in South 
America, as they are at present. The species are in most 
instances distinct from those now living, but the genera are 
nearly the same. The Caviide were especially numerous. 
Cercolabes, Myopotam Ps and. i loc veg oe are nee found, and two 
extinct genera, Phyllomys and Lonchop 
The Cheiroptera, or Bats, have not ae Sacacks in this country 
