X.] ITS FAUNA. 365 



Holarctic and also into Central America. The true raccoons, on 

 the other hand, cannot be regarded as distinctive of the region, 

 since they range from South America into the Canadian sub- 

 region of the Holarctic ; and the coatis (Nasua) are now highly 

 characteristic of the Neogaeic realm. Indeed Dr Merriam con- 

 siders both genera as intruders from the latter realm, but this can 

 scarcely be regarded as the correct view. The family is repre- 

 sented in the two halves of the northern hemisphere (in the eastern 

 by sElurus], in both of which it dates from the Pliocene, and, 

 as it is unknown in South America till the Plistocene or late 

 Pliocene, it is evidently one of northern origin ; the American 

 forms having probably attained their maximum development in 

 the Sonoran region. Much the same is the case with regard to 

 the skunks among the Mustelidcz ; these being probably an original 

 Sonoran type which has spread northwards into the Holarctic 

 region and southwards into the Neogaeic realm. Of these, the 

 single species of climbing skunk (Sptlogale) is mainly Sonoran, 

 although it also enters the Transition zone of the Holarctic, and 

 likewise Central America. Of the other members of the group, 

 the typical skunks (Mephitis) range from Hudson Bay to Guate- 

 mala ; while the allied genus Conepatus is found from Texas to 

 Patagonia. In the same family the American badgers (Taxided), 

 although ranging well into the Holarctic, are regarded by Dr 

 Merriam as of Sonoran origin. These badgers, it may be ob- 

 served, differ from the true badgers of the Old World by the form 

 and characters of their cheek-teeth, the last upper molar being 

 proportionately much smaller. 



Turning to the rodents, the well-known prairie -marmots 

 ( Cynomys], which occupy a position intermediate between the true 

 marmots and susliks, are regarded by Dr Merriam as of Sonoran 

 origin, although they extend into the Holarctic. In the Muridce 

 the peculiar cricetine genus Rhithrodontomys which, together with 

 the allied South American Rhithrodon, differs from the other 

 members of the sub-family to which it belongs by its grooved 

 upper incisors appears to be restricted to the region under con- 

 sideration. The white-footed mice (Sitomys), although distributed 

 over the whole of the New World, seem to attain their maximum 

 specific development in the Sonoran, to which the two sub-genera 



