AMERICAN TURTLES 
133 
geographical interest. Four species o.ccur in North America, 
three of them being limited in distribution to the eastern 
States. Only one, viz.: Clemmys marmorata, is quite con¬ 
fined to the rivers and ponds west of the Cascade and Sierra 
Nevada Mountains in Oregon and California. In Central 
and South America the genus is unknown, but in eastern 
Asia we find four species. One of them inhabits Japan, 
another the island of Hainan, and a couple of them China. 
Far away in western Asia we meet with another species in 
Persia and Mesopotamia, spreading across Asia Minor to 
Greece and Turkey, while finally Clemmys leprosa lives in 
Spain, Portugal and north and western Africa as far as Sene- 
gambia. The genus is thus quite confined to the northern 
hemisphere. We might suppose that the ancestor of the 
American Clemmys insculpta had spread northward from 
eastern Asia in Pliocene times and, after crossing the Bering 
Strait land bridge, had invaded Alaska and Canada, ulti¬ 
mately reaching the eastern States of America in that 
manner, and subsequently becoming extinct in the vast tract 
of country which now separates the Chinese from the eastern 
American species. The south-western Clemmys marmorata 
would thus have been the latest development of the genus 
in America. Such a supposition seems unlikely, owing 
to the unsuitability of the western States for such 
turtles. The few that now inhabit the west are rather to he 
regarded as ancient survivals of a long-distant age when 
the climatic conditions vtere much more favourable for them 
than at present. The earliest member of the genus indeed 
(C. morrisiae), is found in a western Eocene deposit (Bridger 
beds), and Dr. Hay * expresses the opinion that North 
America is probably the original home of Clemmys. If so, 
the genus could not possibly have spread to Asia, and thence 
to western Europe in Pliocene times. The existing centres 
of distribution must have become established during much 
more remote geological periods. Anyhow, although the 
majority of the American species of Clemmys are now con¬ 
fined to the east, we have ample palaeontological evidence 
of its having formerly lived in the west. 
Hay, 0. P., “ Fossil Turtles of North America,” p. 290. 
