II.] RODENTS. 41 



in the Philippine group, where there is one genus allied to 

 Hydromys, while other species have been assigned to the genus 

 Xeromys. Whereas the typical Australian representative of the 

 latter has but two pairs of molar teeth, one of the Philippine 

 forms has three, thus approximating to more ordinary murines. 

 The occurrence of these Australian types of rats in the Philippines 

 is of the utmost importance in respect to Australia having received 

 its mammalian fauna from south-eastern Asia. 



Of the typical genus Afus, whose geographical distributional 

 area includes the whole of the eastern hemisphere with the ex- 

 ception of Madagascar and many of the Polynesian islands 1 , 

 Australia has upwards of twenty-six representatives, while two 

 species occur in the Duke of York group, and others probably on 

 the Papuan mainland. One of the Duke of York species (M. 

 prcetor) ranges eastwards into the Solomons, where three other 

 kinds are also found. The jerboa-rats (Conilurus*) form a pe- 

 culiar saltatorial group restricted to the sandy deserts of the 

 mainland of Australia, where they are represented by about a 

 dozen species ; while the broad-toothed rat (Mastacomys) is con- 

 fined to Tasmania, although its fossilised remains, like those of 

 the other genus, are met with in the caverns of New South Wales. 

 More nearly allied to the true rats and mice, the mosaic-tailed rats 

 (Uromys) inhabit Queensland and the Aru Islands, one of the 

 species from the former area also occurring in the Solomons. 

 Lastly, the prehensile-tailed rat (Chiruromys], from the mountains 

 of south-eastern New Guinea, represents a genus distinguished 

 from all other placental mammals of the eastern hemisphere, 

 with the exception of the British harvest-mouse and the Oriental 

 binturong, by the prehensile nature of its tail. 



In connection with these rodents it is important to observe 

 that fossil Murida are unknown from any part of the world earlier 

 than the Miocene epoch, so that it is evident the living Australian 

 representatives of the family are comparatively recent immigrants 

 into the region they inhabit. 



1 The Pacific rat (Mus exulans) appears to be widely distributed in these 

 islands, see note on p. 29. 



2 Commonly known by the preoccupied name Hapalotis. 



