400 
PAL.EARCTIC REGION AND SUB-REGIONS. 
regions, for while in the Californian snh-region we meet with a pre- 
ponderance of comparatively highly organized belogonons species, 
comparable with those of Japan and China, the more remote eastern 
slope, or Alleghanian snh-region, chiefly displays fine and nnmerons 
representatives of primitive protogonous types, comparable to those 
of South Africa, South America or Australia, while the arid Central 
sub-region is chai’acterized by the possession of large examples of the 
even more archaic Haplogonous Ilelicoids. 
The Pal.earctic region, as restricted, is the largest of the zoological 
divisions, and extends from the sonthern limit of the Arctic zone on 
the north to the Himalayas and the Sahara in the south, and em- 
braces the whole extent of the Eastern Hemisphere from the Atlantic 
to the Pacific. 
To express the difl’erences in the character of the fauna, this enormous 
tract of country has been divided into three sub-regions : Mongolian, 
^lediterranean, and European. 
The IMongolian sub-region embraces the bleak and barren wastes 
of Tartary and the elevated mountain regions of Central Asia, 
including the district around Lake Baikal, which retains so many 
archaic forms of molluscan life. The more arid parts of the snh-region 
are occn])ied chiefly by the weaker Xerophiloid forms, characterized 
by whitish coloration and distinct sculpture, while the more fertile 
country further to the north is occupied by Fruticiculoid forms, allied 
to those of Europe, the whole fauna being more nearly related to the 
North American fauna or to the European post-tertiary deposits, 
rather than to the existing fauna of middle Europe. 
The Mediterranean sub-region includes the countries encircling 
the ^lediterranean Sea and extends eastwardly to Persia and Afgha- 
nistan, and is separated from the stronger North Central European 
region by the interposition of great monntain chains, which are a 
powerful obstacle to the rapid diffusion of improved races ; this sub- 
region is characterized by the development of the relatively simjile 
species of the genera Cumpijlivd, Ilelia'lla, etc., which show a wealth 
of species within this area, and also retains within its limits many 
more species less advanced in development than are found within the 
area of the more vigorous North Central sub-region. 
The European sub-region is bounded on the south by the mountain 
chains which separate it from the Mediterranean region, on the north 
by the southern boundary of the arctic region, on the west by the 
