4 8o RODENTIA 



Subfamily Zapodinse. — Molars rooted ; p \, m § ; cervical ver- 

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

 with five digits. Nearctic region. 



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

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

 dor to Mexico. 



Subfamily Dipodinse. — Molars rooted ; p ~^ y m § ; cervical 

 vertebra? more or less ankylosed ; hind limbs elongated ; metatarsals 

 united ; hind feet with only three functional digits. Palsearctic 

 and Ethiopian regions. 



This subfamily includes the true Jerboas, and contains three 

 genera: Z^Ms 2 with three toes, and Aladaga 3 and Platycercomys * 

 Avith 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. 



Remains of the existing Aladaga 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. Vertebras : C 7, D 12, L 7, S 3, C 30. Ethiopian region. 



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

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

 Cape of Good Hope. 



Section Hystricomorpha. 



Skull (Fig. 213) Avith a stout zygomatic arch; jugal not sup- 

 ported beloAA' by a continuation of the maxillary zygomatic process ; 

 infraorbital \-acuity large ; mandible Avith the angular part arising 

 from the outer side of the bony socket of the loA\ r er incisor. 

 Clavicles perfect or imperfect ; fibula distinct. One premolar in 

 each jaw. 



Family Octodontid^:. 



Clavicles complete. Skull Avith long incisive foramina extend- 

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

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

 Ctenodadylus. Mamma? placed high up on the sides of the body. 

 Confined to the Ethiopian and Neotropical regions, AAdth 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. Pelersbourg, 1844, p. 209. 

 5 = A. jaculus, Auct. B Illiger, Prodromus Syst. Mo nun. p. 81 (1811). 



