478 RODENTIA 
Subfamily Bathyergine.—Angular part of the mandible arising 
from the side of the socket of the lower incisor. Premolars absent 
or present. Confined to the Ethiopian region. 
Bathyergus.1.—Upper incisors strongly grooved; p 4, m 3; no 
ear-conchs ; very powerful claws. One species (B. maritimus), from 
South Africa, attaining a length of about 10 inches. 
Georychus? and Alyoscalops.s—-Upper incisors without grooves. 
Georychus, with some half dozen species, generally has p +; Myo- 
scalops, with one species, usually has p 3, and the second toe of the 
foot is the longest. In Georychus the premolar may be wanting, 
and some examples of Myoscalops have only two teeth of this 
series. 
Heterocephalus.s—Small and nearly naked forms, with small 
head, small eyes, no ear-conchs, moderately long tail, and powerful 
fore feet provided with a pair of large pads; p 2, m =. Two 
species. These very remarkable little Rodents are regarded by 
Mr. O. Thomas as very closely allied to Georychus, but specialised, 
and, so to speak, somewhat degraded for a purely subterranean life, 
for which their hairless body is peculiarly adapted. They are 
found in Somali-land, where they burrow in the sandy soil. 
Family GEOMYID&. 5 
Terrestrial or fossorial forms, with large cheek-pouches opening 
on the cheeks outside the mouth. Squamosal much expanded, 
and the jugal extending forwards to the lachrymal. P21; molars 
rooted or rootless, with transverse lamine. Nearctic and Neo- 
tropical regions. 
Subfamily Geomyine.—lIncisors broad ; mastoid not appearing 
on the top of the skull; eyes small; ear-conch rudimentary ; limbs 
short, subequal. Habits fossorial. 
Geomys.’—U pper incisors deeply grooved. The common North 
American Pouched-Rat or “Pocket-Gopher ” (@. bursarius) inhabits 
the plains of the Mississippi and lives in burrows. Several other 
species are recognised from the Southern United States, Mexico, 
and Central America. The genus is represented in the Pleistocene 
and Pliocene of the United States. 
Thomomys.'—Upper incisors plain. Represented by two species, 
1 Nlliger, Prodromus Syst. Mamm. p. 86 (1811). 
® Tlliger,, Zoe. cit. p. 87. 
2 0. Thomas, Proc. Zool. Soc. 1890, p. 448 = Heliophobius ; Peters, Monatsber. 
Ak. Berlin, 1846, p, 243.—Preoceupied. 
* Riippel, Mus, Senkend. vol. i. Siugeth. p. 99 (1834). 
5 Including the Saccomyide of Coues. 
® Rafinesque, Amer. Monthly Mag. vol. ii. p. 45 (1817). 
7 Wied, Nova Acta Ac. Ces. Leop.-Car. vol. xix. pt. i, p. 383 (1839). 
