MILLER AND GIDLEY: SUPERGENERIC GROUPS OF RODENTS 443 



Subfamily Zapodinae. — Cheekteeth subhypsodont,| or f , flat crowned, 

 the enamel pattern of the upper molars heptamerous, slightly or con- 

 siderabh' modified; external form saltatorial, the hind legs and feet 

 lengthened. 



Eozapus, Recent, China; Zapus, Napaeozapus, Pleistocene and 

 Recent, North America. 



Family Dipodidae 



Like the Zapodidae but with the inner and outer metatarsals reduced 

 or absent and the three median fused to form a canon bone; cheekteeth 

 hj^psodont, the heptamerous enamel pattern undergoing modifications 

 most of which are parallel to those taking place in the teeth of the 

 Cricetidae and in the hystricine families. 



Subfamily Protoptychinae. — Upper cheekteeth 4, moderately hypso- 

 dont; pm* a large, functional tooth; skull with relatively broad rostrum 

 and narrow braincase. 



Protoptychus;'' North American Upper Eocene. 



Suhfamily Dipodinae. — Cheekteeth f or f, strongly hypsodont; pm< 

 vestigial; skull with relativelj- narrow rostrum and broad braincase. 



The Dipodidae of authors who recognize the Zapodidae as a distinct 

 famil}^; Pleistocene and Recent; Eurasia and northern Africa. 



Family Ctenodactylidae 



Cheekteeth growing from a persistent pulp, the adult pattern re- 

 duced to a simple ring infolded on one or both sides (parallel: Odo- 

 dontinae) ; external form fossorial. 



Ctenodactylus and related genera from the Mediterranean region; 

 Pliocene to Recent. 



Family Pedetidae 



Cheekteeth subterete, growing from a persistent pulp; all trace of 

 the original crown structure lost, the unworn enamel cap transversely 

 cleft, the adult pattern consisting of a narrow median infold from the 

 paramere extending nearl}' across to opposite side; external form con- 

 spicuousl}'^ saltatorial, but median metatarsals showing no tendency to 

 become reduced or fused. 



Pedetes; Recent; Africa. 



Superfamily BATHYERGOIDAE 



Zygomasseteric structure as in the Dipodoidae except: Angular por- 

 tion of mandible distorted outward to allow passage of a specialized and 



' While Protoptychus is a true dipodid with few primitive characters its exact 

 position is not clear. It may prove to be a member of the Theridomyinae; but 

 for the present we prefer to place it in the Dipodidae on account of its resemblance 

 to the recent genus Euchoreutes. 



