DISTRIBUTION OF INSECTIVORES, BATS, AND RODENTS 271 



fication have recently undergone important changes, and 

 continual discoveries of new species and new alliances are 

 made by several busy naturalists who are engaged mainly 

 on a study of the smaller mammals. Under these circum- 

 stances it is hardly necessary for our present purpose to 

 mention more than the names of most of the twenty-one 

 families which constitute this complicated group, but we 

 shall endeavour to pick out, as we go through them, some 

 of the most noticeable facts connected with the distribution 

 of these mammals. 



Adopting Mr. Thomas's recent classification of the 

 genera of this group 1 (with a few slight deviations) as the 

 best authority, we find the Anomaluridte, a singular 

 group of Flying-Squirrel-like Rodents, at the head of 

 the Order. This family, with its three genera (Anoma- 

 lurus, Idiurus, and Zenkerella), is purely Ethiopian, 

 the eleven or twelve species which are referred to it 

 occurring only in tropical Africa. Passing on to the next 

 family, the Squirrels {Sciuridze), we have an extensive 

 group of about 240 species divided into eleven genera 

 distributed nearly all over the earth's surface, with the 

 exception of the Australian Region and Madagascar, where 

 they are entirely deficient. The most numerous genus is 

 that of the true Squirrels (Sciurus) which, subject to the 

 exception just mentioned, is fairly distributed over the 

 whole of the earth. 



The Castoridm, or Beavers, which come next, are 

 represented in the present day only by the genus Castor, 

 with two species, one of which occurs in the high latitudes 

 of the Pakearctic and the other in those of the Nearctic 



1 " On the genera of Rodents," P. Z. S. 1896, p. 1012. Cf. Palmer, 

 " Science," N. S., vi., p. 103 (1897). 



