SPECIES OF MAMMALS OF THE PACIFIC AREA 119 



name water rats implies, most of the members of this subfamily 

 are aquatic. Exceptions are a small species {Xeromys myoides) 

 from Queensland, Leptomys and Paraleptoinys, and probably 

 Baiyankamys from New Guinea. True water rats are found 

 also on the adjoining islands, New Guinea, New Britain and 

 Kei, Aru and D'Entrecasteaux Islands, in addition to Australia. 

 Celcenomys, Chrotomys, and Crunomys of Luzon — the last 

 also in Mindanao, the Philippine Islands — are thought also to 

 belong with the water rats. The molar teeth of Chrotomys are 

 basined like Hydromys but they are three in number instead of 

 two. Chrotomys is strikingly marked with a bright buff stripe 

 from head to rump, bordered by black. Crunomys agrees with 

 the common rats in tooth pattern, but the flattened shape of 

 its skull suggests modification for life in water. Celoenomys is 

 slaty gray ; it agrees with Hydromys in having only two cheek- 

 teeth on each side above and below and in the basined character 

 of the teeth. These Philippine rats may be distantly related to 

 the Australian forms or the resemblances may indicate con- 

 vergence. 



Voles, American Rats and Mice 

 Family Cricetid^ 



The voles of the northern hemisphere and the rats native to 

 the western hemisphere differ from true rats by having only 

 two rows of cusps on the upper molars, instead of three. When 

 the teeth wear down, these cusps form a more or less distinct 

 zig-zag pattern, instead of cross-ridges. Although this differ- 

 ence seems small, it has characterized the two groups for millions 

 of years. 



The Red Lemming (Lemmus), which is probably to be found 

 on the landward islands of the Aleutians, is a small, thick-set 

 rodent with short hairy tail, small ears, and long, soft fur. The 

 body color is rusty, grizzled on the head and shoulders. Locally 

 this lemming may become abundant, but over much of its range 

 it is scarce, at least during certain years. It is a close relative 



