VERTEBRATA: MAMMALIA. 759 



sea, and ending in the drowning of all that have survived the 

 journey. 



The Gerbilles (Gerbillus), though closely related to the 

 Jerboas, are generally placed in this family. Here also may 

 be placed the Musquash or Ondatra (Fiber zibethicus) of North 

 America, which leads a semi-aquatic life, and has the tail com- 

 pressed, and the hind-feet partly webbed. 



Fam. 12. Dipodidcz. The next family of the Rodents is that 

 of the Dipodidcz or Jerboas, mainly characterised by the dis- 

 proportionate length of the hind-limbs as compared with 

 the fore-limbs. The tail also is long and hairy, and there 

 are complete clavicles. The Jerboas live in troops, and 

 owing to the great length of the hind-legs, they can leap 

 with great activity and to great distances. They are all of 

 small size, and inhabit Russia, North Africa, and North 

 America. The best-known members of this family are the 

 common Jerboa (Dipus ^Egypticus} of Africa and south-west- 

 ern Asia, which lives in societies and constructs burrows ; 

 the Jumping Hare (Pedetes Capensis] of South Africa, and the 

 Jumping Mouse (Zapus or Meriones Hudsonicus] of North 

 America. 



Fam. 13. Myoxidce. The members of this family are com- 

 monly known as Dormice, and they are often included in the 

 following family of the Squirrels and Marmots. They only 

 require to be mentioned, as they must not be confounded with 

 the true Mice (Muridce) on the one hand, or the Shrew-mice 

 (Soriridce) on the other; the latter, indeed, belonging to an- 

 other order (Insectivora}. The common Dormouse (Myoxus 

 avellanarius] is a British species, and must be familiarly known 

 to almost everybody. No species of this family have yet been 

 described from the New World. In form, the Dormice are 

 Squirrel-like, with a long and hairy tail. There are four rooted 

 molars on each side ; the pollex is rudimentary; and the intes- 

 tine is destitute of a caecum. 



Fam. 14. Sduridcz. This is one of the most characteristic 

 and familiar of the divisions of the Rodents, and it comprises 

 the true Squirrels, the Flying Squirrels, and the Marmots. 

 The molars are rooted, five in number in the upper jaw on 

 each side (the first being often deciduous), and four on each 

 side of the lower jaw ; their crowns, when unworn, being 

 tuberculate. 



The true Squirrels (Sdurus) are familiarly known in the 

 person of the common British species (Sdurus vulgaris), and 

 the equally common Grey Squirrel (S. cinereus] of the United 

 States. Numerous species (about one hundred in number) 



