28 GEOGRAPHICAL DISTEIBUTION. 



genus Myogale, the water-mole, already referred to, which em- 

 braces two species, one of which, M. Pyrenaica, is an inhabitant of 

 the northern valleys of the Pyrenean chain of mountains, and the 

 other, M. Muscovita, the plains of Southeastern Russia skirting the 

 Don and Volga rivers. The pikas (Lagomys), small rodent animals 

 having a ratlier near relationship with the hares, which are exten- 

 sively distributed along the upper mountain heights from the Ural 

 to Cashmere and the eastern extremity of Siberia, have a single 

 outlier in the Rocky Mountains of North America. The members of 

 the genus Capra — the goats and ibexes — occupy disjointed patches 

 of territory in Europe, Asia, and Africa, mainly confined to the 

 elevated mountain regions, such as the Pyrenees, the Sierras of 

 Spain, the Alps, Caucasus, Himalayas, «fcc., the intervals between 

 which are deficient in the wild or indigenous representatives of the 

 genus. A similar discontinuity is exhibited in the case of the 

 snow-partridges of the genus Tetraogallus, a bird likewise partial 

 to the elevated mountain-slopes. Numerous other instances of 

 birds occupying discontinuous areas may be cited, and they appear 

 particularly noticeable among families of a more or less tropical 

 habit. Such, for example, are the ja^anas (Parra), which inhabit 

 the tropical regions of both the Old and the New World, the simi- 

 larly distributed fiamingoes (Phosnicopterus), the wood-ibises of 

 the genus Tantalus, the gerontics (Geronticus), and the marabou 

 storks (Mycteria). Among perching birds a most remarkable in- 

 stance of generic discontinuity has been cited by Wallace in the case 

 of the blue magpies (Cyanopica), which comprise two species, one of 

 which, C. Cookei, inhabits the Spanish Peninsula, and the other, C. 

 cyanus. Eastern Siberia, Japan, and North China, the habitats of 

 the two being removed from each other by an interval of fully 5,000 

 miles. Still more marked is the case of the bluebirds constituting 

 the genus Sialia, all of whose members, with one exception, inhabit 

 temperate and tropical America ; a solitary form, Sialia (Grandala) 

 ccelicolor, singularly enough, crops up again among the Himalaya 

 Mountains, and eastward throughout the mountainous region sepa- 

 rating China from Thibet.* The most remarkable instance of a 

 mammalian genus occupying two widely - removed areas is fur- 

 nished by Tapirus, the tapir, several species of which are natives 

 of the South American continent, and one, very distmct from the 

 others, of Malacca and Borneo, the group of animals, therefore, 



