Descriptions of East Asiatic Mammals 301 
set of characteristics which seem to fit them more completely for 
leaping about in great, open, arid spaces. Some of them, much 
like the kangaroos and wallabies of the Australian deserts, have 
undergone reduction in the number of toes on the hind feet. 
Others have enlarged all parts of the skull which have to do 
with hearing to almost balloon-like proportions, or have large 
ears and capacious cheek pouches. They are inveterate diggers 
or burrowers, using the large, powerful claws on their front 
feet. It is regrettable that more of these amazing rodents do not 
occur in the areas dealt with in this book. Of the several genera 
found in western China, only Allactaga, a Five-toed Jerboa, 
enters the western edge of the coastal strip being discussed. It 
extends eastward to about 126°, near the Gulf of Pechili of the 
Yellow Sea. 
The Siberian Five-toed Jerboa, Allactaga sibirica, is about 
the size of a Roof Rat; the head and body is 5 to 6 inches long, 
Fig. 62. Five-toed Jerboa, Allactaga sibirica. 
