480 RODENTIA 
Subfamily Zapodinze.—Molars rooted ; p 1, m 2; cervical ver- 
tebre free ; hind limbs elongated ; metatarsals separate ; hind feet 
with five digits. Nearctic region. 
Zapus.i—The American Jumping-Mouse (Z. hudsonianus) ex- 
tends over almost the whole North-American continent from Labra- 
dor to Mexico. 
Subfamily Dipodinze.— Molars rooted ; p oxy m %; cervical 
vertebre more or less ankylosed; hind limbs elongated; metatarsals 
united ; hind feet with only three functional digits. Palearctic 
and Ethiopian regions. 
This subfamily includes the true Jerboas, and contains three 
genera: Dipus? with three toes, and Alactaga* and Platycercomys * 
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. 
Remains of the existing Alactaga decumana® 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 Pedetinze.—Molars rootless ; cervical vertebre free ; 
hind limbs elongated; metatarsals separate ; hind feet with four 
digits. Vertebre: C7, D12,L7,83, C30. Ethiopian region. 
Pedetes,® 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) with a stout zygomatic 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 OcTODONTIDE. 
Clavicles complete. Skull with long incisive foramina extend- 
ing into the maxille ; and usually an inferior angle to the Jugal. 
Molars with external and internal enamel-folds; p 3, except in 
Ctenodactylus. Mamme 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. Pétersbouwrg, 1844, p. 209. 
5 = A, jaculus, Auct. _ © Mliger, Prodromus Syst. Mamm. p. 81 (1811). 
