DIPODID^!. 391 



Habits. Similar to those of A. himalayanus and other marmots. 

 The call, however, is different ; Adams describes it as a loud wailing 

 cry, Lydekker as a long screaming whistle of great shrillness. A. 

 caudatus inhabits comparatively fertile localities on the border of 

 the dry region, and is found at a lower elevation than A. hima- 

 layanus, 



Other Central- Asiatic species of marmot are A. dichrous from 

 Northern Afghanistan, A. aureus fioin the mountains west of 

 Tarkand, both allied to A. caudatus but smaller, and A. robustus 

 from Eastern and North-eastern Tibet, allied to A. himalayanus but 

 classed as distinct by Milne-Edwards and Biichner. A Spermo- 

 p7iilus, S. bactrianus, has recently been described by Dr. Scully from 

 Afghan Turkestan. 



Family DIPODID^. 



The present subdivision is composed of the Asiatic and African 

 jerboas, the North- American jumping mice (Jaculus),ihe Cape jump- 

 ing hare (Pedetes), and a few other forms. As a rule they are distin- 

 guished by hind limbs of disproportionate length and a long hairy 

 tail, and both in their form and mode of progression resemble 

 kangaroos. They not only move quickly by jumping on their 

 hind legs, but are said to use their tails to aid their movements. 



The molars have transverse enamel-folds, the incisors are com- 

 pressed. The brain-case is short and broad, the infraorbital opening 

 rounded and very large, the zygomatic arch slender and curved 

 downwards, the malar ascending in front of the orbit to the lachry- 

 mal in a flattened perpendicular plate, the mastoid (supratympanic) 

 part of the bulla generally greatly developed. The elongated 

 metatarsals are united to form a cannon bone. Hind feet with 

 but three functional digits. Cervical vertebra more or less anchy- 

 losed. 



A single species just enters the margin of the Indian area from 

 Central Asia. 



Genus ALACTA.GA, F. Cuv. (1836). 

 Syn. Srirtetes, Wagner. 



On the hind foot there are 5 toes, the first and fifth not reach- 

 ing the ground. Tail long, cylindrical, tufted at the end. Ears 

 long. 



Dentition : i. f, pm. jE|,mfEf' Incisors not grooved; pre- 

 molars small, sometimes lost, two anterior molars in both jaws much 

 larger than the third, and bearing external and internal enamel- 

 folds that become loops with wear. 



