RHIZOMYS RADIUS. 215 



and islands. H. sinicus, Gray, from China, is figured in Hardwicke's 

 Illustrations. 



There are many genera of true i-ats found in the New World, and a 

 few in Africa. From the Old continent there are several peculiar 

 forms, some of which deserve particular mention. Among these are 

 the Hamsters, genus Cricetus. They have the teeth of Murince, but 

 their tail is short and hairy, and they have cheek-pouches. They 

 belong to the Palsearctic region. 



The Beaver, Castor fiber, L., is one of the most remarkable Mttridce, 

 and is, by some, placed in a distinct sub-family. It has four molars on 

 each side, and five toes on all the feet. Its flattened tail, webbed hind^ 

 feet, together with its aquatic habits and peculiar habitations, are 

 described in all popular works on natural history. Their fur is highly 

 prized, and much sought foi', and it is now all but extinct in Europe. 

 The substance called Castor is a peculiar pungent secretion of a glandular 

 pouch, terminating in the prepuce ; and the organs of generation of both 

 sexes terminate within the rectum. 



The genus Helamys, F. Cuvier (Pedetes, Illiger), from South Africa, 

 is a peculiar animal, isolated in its position. It is called the jumping 

 hare, has a large head and eyes, a long tail, short fore-feet, with 5 toes, 

 having long pointed nails ; and lengthened hind-feet, with only four 

 toes, having large claws like hoofs. The Mole-rats, As2xdacid(e, chiefly 

 from Africa, have the incisors broad, large, and exserted ; three molars 

 as in rats, heavy bodies with short limbs and tail, very small eyes, 

 concealed in ome, and the ears small. They live underground, and 

 feed entirely on roots. JSathi/ergus, of South Africa, is made the type 

 of a distinct family by Blyth, Bathyergidce. They have four molars on 

 each side, small eyes, and a short tail. 



The pouched rats are considered by some to form a distinct family, 

 equal in rank to the other four large families. They are the Saccomydidce 

 of authors. They have four molars on each side ; the upper incisors are 

 grooved ; the anterior median nails very long and trenchant. They have 

 deep cheek-pouches, opening externally, and are all from North America. 



Sub-fam. Arvicolin.e, Voles, &c. 



Snout blunt, rounded ; ears small, more or less concealed in the hair; 



3 3 



olars -, composed of alternating tri 



3 — 3 



roots ; incisors rounded ; tail generallj' short. 



3 3 



molars -, composed of alternating triangular prisms, without 



3 — 3 



