THE ECONOMIST MOUSE. 77 



as distinct species ; — we have seen specimens with the 

 colour of" the under surface in intermediate stages between 

 white and yellow. Length of head and body about 

 twelve inches ; that of the tail nearly as much. The 

 Hydromys is a native of Van Diemen's Land and various 

 small islands in D'Entrecasteaux Channel ; but of its 

 habits we have no detailed accounts. 



The family Arvicolidce. — In this family are compre- 

 hended the Water- Rat, the Lemming, and other Rodents, 

 termed Campagnols, Voles, &c,, distinguished from the 

 MuridcB by having rootless molars, by having the angle 

 of the lower jaw raised, and by certain peculiarities in 

 the structure of the cranium. 



The Economist Mouse (Arvicola ceconomus). 



3—3 



In the genus Arvicola the molars are composite 



o — o 

 with flat crowns, presenting angular enamelled laminae. 

 (Fig. 46.) The ears are moderate, the muzzle obtuse, 

 the tail shorter than the body, and hairy. The Econo- 

 mist mouse is a native of the northern sweep of Siberia, 

 and Kamtchatka. It would appear that the same or a 

 closely-allied species inhabits Iceland. It is a burrowing 

 animal, and constructs beneath the turf narrow galleries 

 which lead to a chamber, in the form of an oven, com- 

 municating with another used as a magazine, in which it 

 stores up food for winter consumption. This consists of 

 bulbous roots, and various grains and berries ; and the 

 quantity of provision amassed is often very considerable. 

 These animals breed several times in the year, producing 

 three or four at a birth. Like the lemming, from some 

 unknown cause, these mice, at irregular periods, but 

 always in the spring, perform extensive migrations. 

 Multitudes assemble together, forminof an army myriads 

 strong. In Kamtchatka their progress is westward ; 

 neither rivers, nor lakes, nor even arms of the sea stop 

 them ; thousands are drowned or destroyed by birds and 

 beasts of prey, — but onwards the army marches, — pur- 



VOL. IV. E 



