486 CAPE JUMPING HARE CHAP. 



Alactaga is much like Euchoreutes ; it has five toes, a 

 cylindrical tufted tail, the hairs at the end distichous, smooth 

 incisors, and a premolar present in the upper jaw. It also 

 differs from Euchoreutes by the much smaller auditory bulla as well 

 as in the fact that the infra-orbital foramen has no separate 

 passage for the nerve, which passage is to be distinguished in 

 both Dipus and Euchoreutes. The best-known species is the 

 Siberian Jumping Rabbit, A. jaculus. Beneath the ends of the 

 three main toes of the feet are remarkable fan-shaped pads. In 

 A. decumana the body and tail measure 7 and 1 inches re- 

 spectively, the ears 2 inches. Platycercomys, a fourth genus of 

 the family, is much less known and is to be differentiated from the 

 last three genera by the fact that it has no premolars at all, the 

 grinding tooth formula being thus -f. The tail too is flattened 

 and " lancet shaped." It extends from Siberia to Kubia, and 

 thus just enters the Ethiopian region. 



The above are the more typical Jerboas. There remain 

 several forms which are not at all Jerboa-like in their way of 

 life, but are nevertheless, on anatomical grounds, placed with 

 them. Zapus, an American genus, with the exception of one 

 Palaearctic species, is transitional in that -its hind-legs are 

 rather long, but there is not so much difference between them as 

 in the typical Dipodidae. Sminthus is at the opposite extreme 

 to Dipus. Its feet are short and of equal length ; it climbs in 

 trees, and may perhaps be looked upon as nearest of all Dipodidae 

 to the ancestral form of the group. 



Fam. 8. Pedetidae. The genus Pedetes contains but one 

 species, P. ca/er, the Cape Jumping Hare. The animal suggests 

 a large Jerboa in appearance on account of its jumping habits, 

 the long hind-limbs, and the long tail. The length of a fair- 

 sized example is some 1 7 inches, with a tail of the same length. 

 The eyes and ears are large. The hands are five-fingered and 

 the feet only four-toed, the hallux being of course the absent 

 digit. In the skeleton it is interesting to note that the second 

 and third cervical vertebrae are so close together that there can 

 be no free movement ; interesting because in Dipus the cervicals 

 are actually ankylosed. The dorsal vertebrae are twelve. The 

 small intestine is long, measuring 7 feet 4 inches, while the 

 caecum is short, being only 8 inches long. The large intestine 

 is 3 feet 10 inches long. The gall-bladder appears to be 



