358 



SCIURID^. 



Form heavy, cylindrical, mole- 

 like ; limbs short, tail short or 

 rudimentary ; infraorbital fora- 

 men small, lower maxillary zy- 

 goma-root not flattened 



B. Angular portion of mandible arising 

 from outer side of bony socket of 

 incisor. Fibula distinct. Zygo- 

 matic arch stout 



Body more or less covered with spiues. 



4. Spalacidae. 



Myoxidae (Palsearctic and 



Africa). 

 Lophiomyidae (Africa). 

 Geomyidae (^Vmerica). 



HYSTRICOMORPHA. 



5. Hystricidae. 

 fOctodontidae. 

 I Chinchillidae. 

 (South America.) <( Dasyproctidae. 

 I Dinomyidae. 

 l^Caviidae. 



Family SCIUKID^. 



The squirrels, flying-squirrels and marmots, forming the present 

 family, are distinguished by the following characters : — Tail hairy. 

 Skull with distinct postorbital processes ; infraorbital foramen 



Fig. 119. — Skull of Sciu7-us bicolor, X |. 



small ; palate broad ; premolars ^, the anterior upper premolar 

 small, sometimes deciduous ; molars rooted, tubercular in young 

 animals, the crowns w^hen worn exhibiting deep and often wavy 

 folds of enamel. 



There are two subfamilies thus distinguished : — 



A. Form slender, tail long, incisors compressed ; 



chiefly arboreal SciariiKv. 



B. Form stout, tail generally short, incisors not 



compressed; terrestrial Arctomyime. 



