CITELLUS 721 



eastwards to the Central United States, and from Arctic 

 Alaska southwards to Central Mexico. Although obviously 

 of ancient standing, no fossil remains of the genus have been 

 found, in either Eurasia or America, in deposits older than 

 the Pleistocene. 



The members of the genus Citellus may be regarded as 

 degenerate squirrels. They have forsaken arboreal habits, 

 and have colonised the treeless wastes. In these desert places 

 they are strictly earth-bound animals, leading a great part 

 of their lives in their burrows, and subsisting upon coarse 

 herbage, varied with bulbs, seeds, and grain when available. 

 They devour large numbers of insects, and like the true 

 Squirrels betray carnivorous tastes whenever an opportunity 

 presents itself. They form subterranean stores of provisions 

 for use in inclement weather. In warm countries they remain 

 active at all seasons of the year, but throughout the greater 

 part of their range the Sousliks hibernate regularly, remaining 

 in a torpid state in cold regions for a period of six months 

 or more. 



The acquisition of such habits has, of course, brought 

 about a good deal of modification in bodily structure. Sousliks 

 are animals of medium size. In general outward form they 

 are essentially of sciurine aspect, although they are more 

 robustly built than are most arboreal squirrels, and have 

 relatively shorter peripheral parts. The fur is thin, coarse, 

 and adpressed. The eyes are large. The ears very small 

 (except in some American forms), clothed with numerous 

 short and fine hairs, but without tufts. Cheek-pouches are 

 present. The limbs are much shorter than in Sciurus, and 

 in both hands and feet digit 3, instead of digit 4, is the longest. 

 The vestigial thumb bears a small flattened nail ; the other 

 fingers are long, and armed with long, strong, and rather 

 straight claws well adapted for digging. In the foot all 

 five toes possess similarly shaped though shorter claws. The 

 palms and soles, except towards the heel, are naked ; on the 

 palm there are five pads, on the sole four, the posterior two 

 being absent ; the under surfaces of the digits are annulated. 

 The upper surfaces of hands and feet are well clothed with 

 numerous long hairs which show a tendency to develop as 



