86 MAMMALIA. 



of a reddish-grey. In winter they construct, on the ice, a hut of earth, in 

 which several of them reside together, passing through a hole in the bottom, for 

 the roots of the acorns, on which they feed. They neither dive nor swim well. 

 It is this habit of building which has induced some authors to refer the 

 Ondatra to the genusCajfor : The second subdivision is that of 



ARVICOLA, Cuvier. HYPUDJEUS, flliger. 



Our common Field Rats, which have a hairy tail, about the length of the 

 body, and simple or not palmated feet. 



A. arvalis. (The Campagnol.) Size of a mouse; of a reddish ash-colour; 

 tail not so long as the body. It inhabits holes which it excavates in the earth, 

 where it collects grain for the winter. The multiplication of tin's animal is 

 sometimes so excessive as to cause much injury. 



GEORYCHUS, Illtger, 



Or the Lemmings, Cuv., have very short ears and tail, and the toes of the fore 

 feet peculiarly well formed for digging. 



G. lemmut. (The Lemming.) A northern species, as large as a rat, with 

 black and yellow fur, very celebrated for its occasional migrations in innu- 

 merable bodies. At these periods they are said to march in a straight line, 

 regardless of rivers or mountains ; and while no obstacle can impede their 

 progress, they devastate the country through which they pass. Their usual 

 residence appears to be the shores of the Arctic Ocean. 



G. Hudsonius ; Mus. Hudsonius, Gm., Schreb. (The Lemming of Hudson's 

 Bay.) A light pearly ash-colour; without tail or external ears; the two 

 middle toes of the fore foot of the male seem to have double claws, which is 

 owing to the skin at the end of the toe being callous and projecting from under 

 the nail, a disposition of the part hitherto unknown, except in this animal. It 

 is the size of a rat, and lives under ground, in North America. 



OTOMYS, Fred. Cutter. 



The Otomys are nearly allied to the Field Rats, and have also three grinders, 

 but they are composed of slightly articulated laminse arranged in file. Their 

 incisors are grooved with a longitudinal furrow, and the tail is hairy, as well as 

 the ears, which are large. 



O. capcnsis, Fred. Cuv. (The Cape Otomys.) Size of a rat; fur marked 

 with black and fawn-coloured rings ; tail a third shorter than the body. 



DIPUS, Gmelin. 



The Jerboas have nearly the same kind of teeth as the true rats, except 

 that there is sometimes a very small one immediately 

 before the upper molars. The tail is long and tufted at the 

 end; the head large; the eyes large and prominent; 

 but their principal character consists in their posterior 

 extremities, which, in comparison with the anterior, are 

 of a most immoderate length, and above all, in the meta- 

 tarsus of the three middle toes, which is formed of one 



