The Fossil Turtles of the Bridget Basin— Hay. 329 
gion extensive erosion, so as to produce hills and valleys, 
some of these old channels would appear again as masses 
of sandstone enclosed by finer sediments. 
The occurrence of abundant fossil remains of mammals 
and of reptiles in nearly all portions of the Bridger beds 
proves that there existed here no great and permanent 
lake. How many mammals or even of turtles are probably 
buried at a distance of ten or twenty miles from the present 
shores of lake Michigan? There can be little doubt that 
most of the animals whose remains we find in the Bridger 
beds lived near the spots where they were buried. They 
were such animals as would be found in a low wooded re- 
gion. They v/ere monkeys and bats, broad-footed uninta- 
theres, horses with developed lateral toes, primitive tapirs 
and rhinoceroses, lizards, snakes, and crocodiles, river and 
marsh turtles. In the streams were gars and amias. The 
fauna was one of the most abundant and varied known in 
the history of the world. Already nearly two hundred 
species of mammals are known. The number of species is 
hardly surpassed by the Upper Eocene deposits of Europe 
or the Santa Cruz ^Miocene of South America. And con- 
stantly new and surprising things are coming to light. 
In the present paper the writer proposes to discuss the 
chelonian portion of the Bridger fauna. 
So far as appears, there is no other place in the world 
from which so many species of turtles have been obtained 
as from these Bridger beds. The number of well-founded 
species now appears to be thirty-nine. With few excep- 
tions, they are forms that have evidently inhabited rivers 
and marshes. ^lany of them are closely related to the ex- 
isting turtles of the rivers and ponds and marshes of the 
Mississippi valley. A few were probably terrestrial species 
which inhabited the surrounding high lands and were swept 
down to their burial places during times of high water. 
Individuals were evidently extremely abundant, and por- 
tions of their skeletons are to be seen almost everywhere. 
Complete shells are, of course, less common, but may be 
had by searching. Shells accompanied by limbs and skulls 
must be regarded as rare, but they too may be found. 
Turtles from i^he Bridger beds have been described by 
