MURIDA 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 MuRIDA. 
Skull (Fig. 203) with contracted frontals ; 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, tuberculate, 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 Hydromyinz.—Molars 2 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 wall 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.® 
Xeromys.t—External form Murine. Tip of muzzle as in Mus, 
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 Plataeanthomyinze.—Molars rooted, with transverse 
1 Sminthus is referred to the Dipodida. 
2 Geoffroy, Ann. du Muséum, vol. vi. p. 81 (1805). 
3 For the anatomy of this animal see B. C. A. Windle, Proc. Zoo/. Soc. 1887, 
p. 53. 4 0. Thomas, Proc. Zool. Soc. 1889, p. 247. 
