94 GEOGRAPHICAL DISTRIBUTION 



to India and Africa. The American Puma, again, may be cited as 

 an example of a mammal having a very wide range in latitude, 

 since it is found from Patagonia in the south to Canada in the 

 north. As instances of wide range in the opposite direction we 

 have only to mention the Eeindeer and the Elk or Moose, found 

 in the northern regions of both the Old and New Worlds, which 

 are only separated from one another by the narrow channel of 

 Behring Strait. 



Of mammals with extremely restricted distributional areas, we 

 may mention many of the Insectivora, such as the Desman of the 

 Pyrenees, and some of the Madagascar types of this order, the 

 Lemurs from the same island, some of the species of Marmots, the 

 remarkable bear-like ^Eluropus of Eastern Tibet, one species of Zebra, 

 and other Ungulates from Africa. 



The distribution of a genus (except of course when the genus is 

 represented only by a single form) is very generally more exten- 

 sive than that of a species ; and this may be markedly the case 

 when there are only some two or three species in a genus. In 

 genera, moreover, we meet with what is known as discontinuous 

 distribution, that is, where the distributional area of one or 

 more species is totally separated from that of others. The best 

 instance of this occurs in the case of the Tapirs, where we find 

 one species inhabiting the Malayan Peninsula, and no others 

 anywhere in the world, with the exception of South America. The 

 explanation of such an apparently anomalous feature in distribution 

 is to be found in the past history of the globe, which shows us that 

 Tapirs once existed in China, Europe, and North America, and, 

 therefore, indicates that the existing isolated species are the sole 

 survivors of a group once spread over a large portion of the earth's 

 surface. In regard to generic distribution it must, however, be 

 mentioned that this depends to a great extent on the limits which 

 we are disposed to assign to genera themselves. 



As the distributional area of a genus generally exceeds that of 

 a species, so that of a family, or group of genera, is larger than that 

 of a single genus ; and similarly the distribution of an order, or 

 assemblage of families, usually occupies a larger area than that of 

 a single family. Thus, for instance, the genus Thylacinus, re- 

 presented only by the so-called Tasmanian Wolf or Thylacine, is 

 now entirely restricted to Tasmania ; but the family Dasyuridce, to 

 which that genus belongs, ranges all over Australia, while the order 

 Marsupialia, which includes the Dasyuridce, is found both in Aus- 

 tralia and America, and in past epochs was probably spread over 

 the entire globe. 



A remarkable feature in connection with the distribution of the 

 terrestrial Mammalia is the circumstance that, with the exception of 

 certain species introduced by human agency, and small forms which 



