358 



SCIUEID.S!. 



c'. Form heavy, cylindrical, mole- 

 like ; limbs short, tail short or 

 rudimentary ; infraorbital fora- 

 men small, lower maxillary zy- 

 goma-root not flattened 4. Spalacidae. 



Myoxidae (Palaearctic and 



Africa). 



Lophiomyidae (Africa). 

 Geomyidae (America). 

 B. Angular portion of mandible arising 

 from outer side of bony socket of 

 incisor. Fibula distinct. Zygo- 



matic arch stout HYSTBJCOMORPHA. 



Body more or less covered with spines. 5. Hystricidae. 



fOctodontidae. 

 I Chinchillidae. 



(South America.)^ Dasyproctidae. 

 I Dinomyidae. 

 Caviidaj. 



Family SCIURTD^E. 



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 Sciurus bicolor, X f . 



small ; palate broad ; premolars ^|, the anterior upper preinolar 

 small, sometimes deciduous ; molars rooted, tubercular in young 

 animals, the crowns when worn exhibiting deep and often wavy 

 folds of enamel. 



There are two subfamilies thus distinguished : 



A. Form slender, tail long, incisors compressed ; 



chiefly arboreal Sciurince. 



B. Form stout, tail generally short, incisors not 



compressed; terrestrial Arclomyince. 



