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 Rat 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 Gerbillus, 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. The incisors are orange; they are white in Dipus. Gerbillus pyramidum is 90 mm. long, with a tail of 125 mm. The ears are long, 13 mm. The tail has longer hairs at the tip.
Fig. 236.—Gerbille. Gerbillus aegyptius. × ½.
Psammomys is in some respects different. The tail is shorter than in Gerbillus; its length in an individual of 165 mm. was 130 mm. As in Gerbillus 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 Gerbillus.
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 Oreinomys, are Ethiopian. Otomys unisulcatus 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 20 mm.
