THE GERBILLES 475 



tion, and the lower incisors are worn to needle-like points. The 

 two molars are excessively minute, and thus the always large gap 

 in the jaws is greatly exaggerated. It is suggested that this Eat 

 is an insect-eater, but nothing positive is known. 



Sub-Fam. 4. Gerbillinae. — The Gerbilles form another sub- 

 family, Gerbillinae, of the Muridae, or a family, according to some. 

 The best-known genus is Orrhillns, including the Gerbilles proper. 

 These animals are Old World in range, belonging to the three 

 regions of that part of the world. There are a large number of 

 species in the genus, over thirty. They have a Jerboa-like form, 

 with rather long hind-limbs and a long and hairy tail. But the 

 hind- as well as the fore-feet are five-toed. The molar teeth have 

 no trace of tubercles, but only transverse lamellae of enamel. 



Fig. 236. — Gerbille. Oerhillns aegyptius. x J. 



The incisors are orange ; they are white in Biims. Gerhillus 

 pyramiduTn is 90 mm. long, with a tail of 125 mm. The ears 

 are long, 13 mm. The tail has longer hairs at the tip. 



Psammomys is in some respects different. The tail is shorter 

 than in GcrUUus ; its length in an individual of 165 mm. was 

 130 mm. As in Gerhillus there are four pairs of teats, two 

 pectoral and two inguinal. This genus is exclusively Palaearctic 

 in range. Meriones has a range co- extensive with that of 

 Gerhillus. 



Pachyuromys is an Ethiopian genus with a short tail. As 

 the generic name denotes, the tail is not only short but thick 

 and fleshy. 



Sub-Fam. 5. Otomyinae. — The allied genera, Otomys and 

 Ordnomys, are Ethiopian. Otomys unisulcatvs has a tail shorter 

 than the body, the measurements of a female of this species being 

 137 mm. with a tail of 87 mm. The ear is long, whence the 

 name ; it measured in this specimen 2 mm. 



