104 MAMMALIA ORDER V.RODENTIA. 



from that of all the other members of the sub-family in having seven 

 prisms. 



Although frequently regarded as representing a sub-family by themselves, 

 the mole-voles, of which there are two genera, may be considered merely as 

 voles specially adapted for a subterranean existence ; the limbs and tail being 

 very short, and the body somewhat mole-like, while the eyes are small. In 

 the genus Mlobius, with one species from Russia, and a second from Afghan- 

 istan, the claws are short, whereas in Siphneus, of which there are several 

 representatives from Central and Northern Asia, those of the fore-feet are 

 enormously powerful. 



In the typical rats and mice and their allies, forming the murine group of 

 the family, the molars are rooted and tuberculated, with three rows of 

 tubercles on at least the anterior ridge of the first one in the 

 Typical Group upper jaw. Indeed, with one exception, there are three longi- 

 (Murince). tudinal rows of tubercles on all the upper molars ; while, save 

 in one genus, there are two such rows in the corresponding 

 lower teeth. The whole group is restricted to the Old World, being re- 

 presented in Australia and New Guinea, but unknown in Madagascar. The 

 great majority of forms are very similar in external appearance, their build 

 being light, their eyes large and bright, their tails long and scaly, their 

 movements active, their coloration sombre, and their habits generally 

 burrowing and nocturnal. 



The least specialised member of the family is a small mouse from the 

 Congo Valley, known as Deomys, which differs from all the others in that only 

 the first ridge of the anterior upper molar has three rows of tubercles, the 

 other two ridges of this tooth and all those of the other molars having but 

 two such rows, as in the cricetines. On the other hand, Berdmore's rat 

 (Hapalomys berdmorei\ from Burma, appears to be the most specialised of 

 all, the lower as well as the upper molars having three longitudinal rows of 

 tubercles. Another peculiar genus (Vandeleuria) is represented by a species 

 extending from India to Yunnan, and characterised by having flat nails on 

 the first and fifth digits of both feet, as well as by the great length of the tail. 

 North-Eastern India and some of the countries to the east of the Bay of 

 Bengal are the home of the pencil-tailed tree-mouse (Chiropodomys), dis- 

 tinguished by having flat nails on the first digit of both feet, whereas all 

 other members of the family, except one species of Mus, have a flat nail only 

 on the first to'e of the fore-foot. The next for notice are three genera re- 

 stricted to the mountains of Luzon, in the Philippine group, two being 

 represented only by a single species. By far the most remarkable of these 

 is the shrew-rat (Rhynchomys), distinguished by the shrew-like prolongation of 

 the muzzle, the short and feeble incisors, and the reduction of the molars, 

 which are very small, to two pairs in each jaw. Not improbably this species, 

 which is of the size of the black rat, and of a uniform olive-grey coloration, 

 subsists on insects or larvse, as the incisors appear too weak for gnawing. 

 The second genus, Carpomys, is represented by two somewhat dormouse-like 

 rats, with thick, woolly fur, and the long tail well haired ; while the single 

 species of Batomys differs by the hind-feet being wider and shorter, and the 

 fore-feet more elongated. 



The true rats and mice constitute a genus (Mus) having a distribution co- 

 extensive with that of the sub-family, and including nearly 150 species. In 

 these Rodents the incisors are narrow and smooth, the molars of the typical 

 murine structure, the foramina at the anterior end of the bony palate 



