1-JO MAMMALIA. 



callous, and forms a projection under the poiat 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. 



Otomys, Fred. Cm. 



The Otomys are nearly allied to the field rats, and have also three 

 grinders, but they are composed of slightly arcuated laminae, arranged in 

 file.* Their 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.-j- 



Dipus, 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. 



f 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 Etinjofis irrorata. 



X 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 t>ip. te.lum, D. pluturus, and D. lagopus of Eversman, Voy. de Mayen- 

 dorf en Boucarie, p. 390. 



