GENEKIC DISTRIBUTIOIT. 27 



among the swimmers, waders, and birds of prey, whose range 

 covers the greater extent of the primary divisions of the earth's 

 surface, and which may, consequently, be said to have a cosmo- 

 politan distribution. Generic groups vdth a nearly world-wide 

 distribution among the Mammalia are of much rarer, although of 

 not exactly infrequent, occmTence, and if the Australian dingo, 

 a species of wild dog, be not considered indigenous to the country 

 which it inhabits, there would appear to be, if we except the bats, 

 not a single altogether cosmopolitan genus among that class of ani- 

 mals. Leaving out of consideration the continent of Australia, 

 whose mammalian fauna is deficient in nearly all the orders of the 

 class, we have a considerable number of genera whose range com- 

 prises the greater portion of the habitable globe.* Thus, the mem- 

 bers of the genus PeUs (cats) are spread throughout the entii-e 

 expanse of the continents of both the Eastern and the Western 

 Hemisphere, through regions the extremes of whose temperatm-e 

 may be measured by probably no less than 225 degrees of the 

 Fahrenheit scale. The genus Canis (dogs) has an almost equally 

 broad distribution ; and the same range -is exemplified in the case 

 of the weasel genus (Mustela). Ursus, the bear, is met with 

 throughout the greater part of the Northern Hemisphere, and in 

 the continent of South America the genus has one or more rep- 

 resentatives whose habitat is situated considerably to the south of 

 the Equator, t The genus Cervus (deer), in its broader sense, has 

 representatives in both North and South America, Europe, and 

 Asia, with a very limited number of species (fallow-deer, stag) in 

 Africa north of the Sahara. 



Discontinuous generic areas, like specific" areas, are of com- 

 paratively rare occurrence. Among the most remarkable instances 

 of such discontinuity we have that exhibited in the case of the 



* The only placental animals indigenous to the Australian continent, if we 

 exclude the rather doubtful dingo, which Is hy most naturalists considered to 

 have been introduced by man, are the Cheiroptera (bats) and Eodentia, the 

 latter represented by the family of mice (Muridse). The implaeental mam- 

 mals — ^kangaroos, wombats, phalangers — ^have, on the other hand, an extraor- 

 dinary development. 



t The solitary species of bear inhabiting the continent of Africa appears to 

 be confined to the Atlas Mountains ; it constitutes the genus Helarctos of 

 some authoi-s (H. Crowtheri). 



