MURID^E 461 



appears doubtful whether that distinction is justifiable. The hair 

 forms a crest along on the back, and is of a peculiar structure. 

 The habits of this Rodent are arboreal. 



Family 



Skull (Fig. 203) with contracted f rentals ; a short and slender 

 jugal, generally reduced to a splint between the zygomatic pro- 

 cesses of the maxilla and squamosal ; the lower root of the former 

 process more or less flattened into a perpendicular plate ; typically, 

 the infraorbital vacuity tall, and wide above and narrow below. 

 Lower incisors compressed ; no premolars ; * molars rooted, or root- 

 less, ttiberculate, or with angular enamel-folds. Pollex rudimental ; 

 tail generally nearly naked and scaly. Habits various, but mostly 

 terrestrial. 



This large and cosmopolitan family, which includes more than 

 a third of the existing Rodents, is represented by about forty 

 genera. 



Subfamily Hydromyinse. Molars f in number, rooted, and 

 divided into transverse lobes. Represented by two Australasian 

 genera. 



Hydromys 2 External form modified for an aquatic life. Tip 

 of muzzle extensively haired, so that the nostrils can be closed. 

 Skull with the infraorbital vacuity crescentic, scarcely narrowed 

 below, and its external Avail without the perpendicular zygomatic 

 plate characteristic of most of the family ; incisive foramina very 

 small. 



Two species, with habits like those of the Water Voles, are 

 known from Australia, Tasmania, and New Guinea. In the 

 typical H. chrysogaster the colour of the back is black, with an 

 admixture of golden -coloured hairs ; the belly being of a dark 

 golden hue. 3 



Xeromys.* External form Murine. Tip of muzzle as in Mm, 

 not as in Hydromys. Toes unwebbed. Tail scaly, very finely 

 haired. Skull as in Mus, with the exception of the rounding of the 

 supraorbital edges. Teeth as in Hydromys. 



Represented by X. myoides, of Queensland ; a species about 

 twice the size of the Common Mouse. This genus serves to con- 

 nect Hydromys with the other Murines, although it is difficult to 

 say to which group it comes nearest. 



Subfamily Plataeanthomyinse. Molars rooted, with transverse 



1 Sminthus is referred to the Dipodidce. 

 " Geoffrey, Ann. du Mustum, vol. vi. p. 81 (1805). 



3 For the anatomy of this animal see B. C. A. Windle, Proc. Zool. Soc. 1887, 

 p. 53. * 0. Thomas, Proc. Zool. Soc. 1889, p. 247. 



