66 CLASS MAMMALIA. 



The Rats, (Mus, L.) 



Linnaeus and Pallas seem to have united in a single 

 group, under this appellation, all the Rodentia pro- 

 vided with clavicles, which have not been distin- 

 guished by any very obvious external mark. From 

 this it results, that it is next to impossible to assign 

 them any common character, unless we have re- 

 course to that of the lower pointed incisors, sug- 

 gested by the first of these naturalists. Still, it 

 will be necessary, for the sake of precision, to sepa- 

 rate, as we do, the Rat-Mole, and the Helamys or 

 Pedetes. The other Rats may then be properly 

 subdivided by the grinders, into many sub-genera, 

 which may all be reunited into three small groups. 



1 . Those which have prismatic molars, or with flat 

 coronals, and crossed to the full extent of their 

 height by plates of enamel, a structure which we 

 again discover in Hares and some other animals, 

 and is observable even in the Elephant. We shall 

 apply to them the generic name of 



Campagnols, Cuv. (Arvicola.) 



All of these which are known have three cheek- 

 teeth in each jaw, and each of them are formed of 

 five or six, and sometimes of eight triangular prisms, 

 placed alternately on two lines. 



The first subdivision comprehends, 



The Ondatras (Fiber, Cuv.), 

 Or Campagnols, with palmate feet, and long 



