chap, ii.] THE ELEMENTARY FACTS OF DISTRIBUTION. 
23 
with the black-headed jay (No. 3), and perhaps the two areas do 
not meet. The Persian jay (No. 5), is quite isolated. The Hima- 
layan and Chinese jays (Nos. 7, 8, and 9) form a group which 
are isolated from the rest of the genus; while the Japanese 
jay (No. 11), is also completely isolated as regards the European 
jays to which alone it is closely allied. These peculiarities of 
distribution are no doubt in part dependent on the habits of the 
jays, which live only in well-wooded districts, among deciduous 
trees, and are essentially non-migratory in their habits, though 
sometimes moving southwards in winter. This will explain 
their absence from the vast desert area of Central Asia, but it 
will not account for the gap between the North and South 
Chinese species, nor for the absence of jays from the wooded 
hills of Turkestan, where Mr. N. A. Severtzoff collected assid- 
uously, obtaining 384 species of birds but no jay. These 
peculiarities, and the fact that jays are never very abundant 
anywhere, seem to indicate that the genus is now a decaying 
one, and that it has at no very distant epoch occupied a larger 
and more continuous area, such as that of the genus Parus at 
the present day. 
Discontinuous generic Areas . — It is not very easy to find 
good examples of genera whose species occupy two or more quite 
disconnected areas, for though such cases may not be rare, we 
are seldom in a position to mark out the limits of the several 
species with sufficient accuracy. The best and most remarkable 
case among European birds is that of the blue magpies, forming 
the genus Cyanopica. One species ( C . cooki) is confined (as 
already stated) to the wooded and mountainous districts of Spain 
and Portugal, while the only other species of the genus (C. cy anus') 
is found far away in North-eastern Asia and Japan, so that the 
two species are separated by about 5,000 miles of continuous 
land. Another case is that of the curious little water-moles 
forming the genus Mygale, one species M. muscovitica, being found 
only on the banks of the Volga and Don in South-eastern 
Russia, while the other, M. pyrenaica, is confined to streams on 
the northern side of the Pyrenees. In tropical America there 
are four different kinds of bell-birds belonging to the genus 
Chasmorhynchus, each of which appears to inhabit a restricted 
