130 MAMMALIA. 
callous, and forms a projection under the point of the nail—a struc- 
ture which has not been met with, except in this animal. It is the 
size of a rat, and lives under ground, in North America, 
Ovomys, Fred. Cuv. 
The Otomys are nearly allied to the field rats, and have also three 
grinders, but they are composed of slightly arcuated lamine, arranged in 
file.* heir incisors are grooved with a longitudinal furrow, and the tail 
is hairy, as well as the ears, which are very large. 
The species known is O. capensis, Fred. Cuv. (The Cape Oto- 
mys). Inhabits Africa. Size of a rat; fur annulated with black 
and fawn colours; tail a third shorter than the body.+ 
Dirvus, Gm. 
The Jerboas} have nearly the same kind of teeth as the true rats, ex- 
cept that there is sometimes a very small one immediately before the up- 
per molars. ‘The tail is long and tufted at the end; the-head large; the 
eyes large and prominent; but their principal character consists in their 
posterior extremities, which, in comparison with the anterior, are of a 
most immoderate length, and above all, in the metatarsus of the three 
middle toes, which is formed of one single bone, resembling what is called 
the tarsus in birds. It is from this disproportion of the limbs that they 
were named by the antients Biped Rats; and in fact they seldom move 
otherwise than by great leaps on their hind feet. There are five toes to 
each of the fore feet; and, in certain species, besides the three great toes 
to the hind feet, there are small lateral ones. They live in burrows, and 
fall into a deep lethargy during the winter. 
D. sagitta; M. sagitta, L.; Buff. Supp. VI. xxxix and xl. The 
Jerbao has only three toes, and is the size of a rat; a light fawn co- 
lour above; white beneath; tuft of the tail black, the tip white. Is 
found from Barbary to the north of the Caspian sea. 
D. hirtipes, Lichtenstein. (The Hairy-footed Jerboa). The head 
more compressed than in the others; only three toes to the hind feet, 
as in the Jerboa, but they are more hairy. From Africa.§$ 
D. jaculus; M. jaculus, Pall. Glir. XX. Schreb. CCXXVIII. 
(The Alactaga). Two small lateral toes; ears longer than those of 
the Jerboa, but,has nearly the same colours. Pallas has observed 
them of three sizes, from that of a rabbit to that of a rat: they are 
* They are exact models, in miniature, of the grinders of the elephant. 
ft It is the same animal described and represented in the essay on the genus of 
rats, by M. Brantz, Berlin, 1827, under the name of Euryotis irrorata. 
{ There has lately appeared an excellent paper on the Jerboas, by M. Lichten- 
stein, in which that learned naturalist describes and figures ten species. I can only 
refer my readers to the paper itself. It is inserted in the Journal of the Acad. of 
Berlin. 
§ Add the Dip. telum, D.platurus, and D. lagopus of Eversman, Voy. de Mayen- 
dorf en Boucarie, p. 390. 
