SPECIES OF MAMMALS OF THE PACIFIC AREA 113 



the house mouse, the body is considerably heavier; its total 

 length is about five and one-fourth inches, of which the tail is 

 about two inches. It is known from Hondo and Shikoku Islands, 

 Japan. 



Old World Rats and Mice. Family Murid^ 



Although the rats and mice of this family belong to the Old 

 World, some of them have spread wherever men are found. Rats 

 and mice of American origin, some of which occur in the Gala- 

 pagos Islands near the coast of South America, together with 

 the northern voles and lemmings of both hemispheres, belong to 

 a different family, the Cricetidae (see p. 119). The only rodents 

 that occur in the South Pacific area between Celebes and the 

 one-hundredth degree west latitude are Old World rats and 

 mice. This is a complex and varied group, basic differences of 

 which reside chiefly in the structure of the skull and teeth. 

 Many of them look like common house rats. Two subfamilies 

 occur on the islands between the Malay Peninsula and Aus- 

 tralia ; only one of these subfamilies, the typical rats, is found 

 east of the Solomons. 



Typical Rats and Mice. Subfamily Murine 



The cheek-teeth of most of these rats are simple, their cusps 

 forming parallel transverse ridges, three ridges on the first 

 molar, two on the other two. Before it becomes worn each ridge 

 consists of three cusps, the central one slightly larger than the 

 outer and inner ones. Although this seems a rather small fea- 

 ture, it has been characteristic of the family for a long period 

 of time. 



The House Mouse (Mus) is so well known that it may be 

 thought unnecessary to describe it. Most specimens found be- 

 tween the Malay Peninsula and the Marquesas Islands are 

 slightly more reddish than the house mice of the United States 

 and western Europe; east of this region and north of it the 

 mice are the same as at home. Adult house mice vary from 



