480 RODENTIA 



Subfamily Zapodinse. Molars rooted ; p , m f ; cervical ver- 

 tebrae free ; hind limbs elongated ; metatarsals separate ; hind feet 

 with five digits. Nearctic region. 



Zapus. 1 The American Jumping-Mouse (Z. hudsonianus) ex- 

 tends over almost the whole North- American continent from Labra- 

 dor to Mexico. 



Subfamily Dipodinse. Molars rooted ; p ^ r , ', 



m 



~5 ) 



vertebrae more or less ankylosed ; hind limbs elongated ; metatarsals 

 united ; hind feet with only three functional' digits. Palaearctic 

 and Ethiopian regions. 



This subfamily includes the true Jerboas, and contains three 

 genera : Dipus 2 with three toes, and Alactaga 3 and Platycercomys 4 

 with five, the outer two not reaching to the ground. The latter is 

 distinguished by the absence of premolars, and comprises many 

 species extending from Siberia to Nubia. 



Eemains of the existing Alactaga decumana 5 occur in the Pleisto- 

 cene of Germany, and those of Zapus hudsonianus in the corresponding 

 strata of the United States. Platycercomys has been recorded from 

 the Pleistocene of Northern Asia. 



Subfamily Pedetinse. ^-Molars rootless ; cervical vertebras free ; 

 hind limbs elongated ; metatarsals separate ; hind feet with four 

 digits. Vertebra : C 7, D 12, L 7, S 3, C 30. Ethiopian region. 



Pedetes, 6 the Cape Jumping-Hare (P. coffer), by far the largest 

 species of the family, extends from Mozambique and Angola to the 

 Cape of Good Hope. 



Section HYSTRICOMORPHA. 



Skull (Fig. 213) with a stout zygoma tic arch; jugal not sup- 

 ported below by a continuation of the maxillary zygomatic process ; 

 infraorbital vacuity large ; mandible with the angular part arising 

 from the outer side of the bony socket of the lower incisor. 

 Clavicles perfect or imperfect ; fibula distinct. One premolar in 

 each jaw. 



Family OCTODONTID^E. 



Clavicles complete. Skull with long incisive foramina extend- 

 ing into the maxillae ; and usually an inferior angle to the jugal. 

 Molars with external and internal enamel -folds ; p ^, except in 

 Ctenodactylus. Mammae placed high up on the sides of the body. 

 Confined to the Ethiopian and Neotropical regions, with the excep- 



1 Coues, Bull. U.S. Geol. Surv. Terrs, ser. 2, No. 5, p. 253 (1873). Syn. 

 Jaculus, "Wagler. 2 Gmelin, Syst. Nat., vol. i. p. 157 (1788). 



3 F. Cuvier, Proc. Zool. Soc. 1836, p. 141. 

 * Brandt, Bull. Ac. St. Petersbaurg, 1844, p. 209. 

 5 = A. jaculus, Auct. 6 Illiger, Prodromus Syst. Mamm. p. 81 (1811). 



