CKAr. 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. 



Discontimmis 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 (G. coohi) is confined (as 

 already stated) to the wooded and mountainous districts of Spain 

 and Portugal, while the only other species of the genus ((7. cyanus) 

 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 



