114 



NATURAL HISTORY. 



MOLAR TEETH OF THE GERBILLE. 



The Gerbilles are plump little animals, with a short neck, a broad head, and a pointed muzzle. 

 The feet are five-toed, but the thumb on the fore feet is reduced to a mere wart-like process with 



a flat nail. They are confined to the Eastern hemi- 

 sphere, and, indeed, to the African continent, the south 

 of Asia, as far as India, and the south-east of Europe, 

 where they live both in. cultivated districts and in the 

 driest deserts, and often occur in great numbers, when 

 they may cause considerable damage to the neighbouring 

 crops. They shelter themselves during the day in shal- 

 low burrows, and come forth in the evening in search 

 of their food, which consists chiefly of grain and roots. 

 They store up great quantities of the ears of corn in 

 their subterranean dwellings, and in many places the 

 poorer inhabitants search after these stores, and by 

 digging them out procure a good supply of grain. They 

 are very prolific, the females producing large families 

 several times in the year. 



Several other forms of Muridse, with rooted molars, have been distinguished, and all are 

 inhabitants of the Eastern hemisphere. The genera Phlceomys and Nesokia, each including a single 

 species, form the group PHL^EOMYIN^E, characterised by 'having broad incisors and the molars divided 

 by transverse plates of enamel. The characters of the skull are as in the Murinse. Phlceomys 

 Cumingii is from the Philippine Islands ; Nesokia Griffithii inhabits Northern India. Platacanthomys 

 lasiurus, the only known species of the group PLATACANTHOMYIN^E, resembles a Dormouse in its form, 

 and is nearly allied to the preceding species, but has the fur of its back mixed with long, flattened, 

 bristle-like spines. It is a native of the Malabar coast. 



The WATER MICE (Hydromyince) are of particular interest, as being a small group, exclusively 

 confined to the Australian region, and presenting the 

 exceptional character among the Rodents of having only 

 two molars on each side in each jaw. These teeth, are 

 rooted, and divided into transverse lobes by ovate enamel 

 lobes ; the front tooth is much larger than its fellow. The 

 Hydromys are small rat-like animals of slender form, with 

 long tails, rather densely clothed with short hairs, and short 

 limbs. The hind feet have much stronger claws than the 

 fore feet, and their toes are partially webbed. Five species 

 of this group are known from Australia and Van Diemen's 

 Land, where they inhabit the banks of the streams. The 



l>est known are the Yellow-bellied and the White-bellied Water Mice (Hydromys chrysogaster and 

 leucogaster), both of which inhabit New South Wales, and the latter is also found in Van Diemen's 

 Land. The Sooty Water Mouse (H. fuliginosus) is an inhabitant of Western Australia. 



In the SMINTHIN^E a group which includes only the genus Sminthus, founded for the reception of 

 a rat-like Rodent (S. vagus) first discovered in the Crimea, but now known to range from Hungary, 



Finland, and Sweden, through Russia to the banks of the Irtisch 

 and Yenisei, and into Tartary (Bokhara) we find another excep- 

 tional character of the molar teeth. There are four of these teeth on 

 each side both above and below, the first and fourth of which are much 

 smaller than the intervening ones. In this animal the ears are rather 

 long and pointed, the legs are rather short, and the tail is about as 

 long as the body, and clothed with short hairs. 



In the remainder of the Muridse, the molars, which are again only three in number on each side, 

 are generally rootless, although occasionally the growth of the teeth stops and they close up below. 

 The molars are composed of triangular prisms placed alternately. Two groups are thus characterised, 

 namely, the Voles and the Zokors. 



SKULL OF THE WATER- MO I' SE. 



TEETH OF SMINTHUS. 



