470 ZOOLOGY. 



Missouri and the prairie towns ; thence to the Platte they were much 

 more numerous. The entrance to the burrow is at the summit of the httle 

 mound of earth brought up by the animal during the process of the excava- 

 tion below. These mounds are sometimes inconspicuous, but generally 

 somewhat elevated above the common surface, though rarely to the height 

 of eighteen inches. Their form is that of a truncated cone, on a base of 

 two or three feet, perforated by a comparatively large hole or entrance at 

 the summit or in the side. The whole surface, but more particularly the 

 summit, is trodden down and compacted, like a well worn pathway. The 

 hole descends, vertically, to the depth of one or two feet, whence it con- 

 tinues in an oblique direction downwards. A single burrow may have 

 many occupants. We have seen seven or eight individuals sitting upon 

 one mound. The burrows occur usually at intervals of about twenty feet. 

 They delight to sport about the entrance of their burrows in pleasant 

 weather. At the approach of danger they retreat to their dens, or when its 

 proximity is not too immediate, they remain, barking and flourishing their 

 tails, on the edge of their holes, or sitting erect to reconnoitre. When 

 fired upon in this situation, they never fail to escape, or, if killed, to fall 

 into their burrows, where they are beyond the reach of the hunter. As 

 they pass the winter in a lethargic sleep, they lay up no provision of food 

 for that season, but defend themselves from its rigors by accurately closing 

 up the entrance of the burrow. The farther arrangements which the 

 prairie dog makes for his comfort and security are well worthy of attention. 

 He constructs for himself a very neat globular cell with fine dry grass, 

 having an aperture at the top large enough to admit the finger, and so 

 compactly formed, that it might almost be rolled over the floor without 

 injury." 



The genus Tamias (the ground squirrels) is very nearly allied to the 

 squirrels proper (Sciurus), from which it differs by many particulars, among 

 which is the presence of ample cheek-pouches, a longer head, the ears placed 

 further back, a more slender body, and shorter extremities. The ears 

 themselves are rounded, and without any tufts on the edge or behind them. 

 The tail is shorter than the body, rounded, narrow, seldom turned wp. 

 There are four toes to the fore feet, with a minute blunt nail in place of a 

 thumb, and five to the hind ones. The claws are hooked. Two incisors 

 above and two below, smooth, the lower ones compressed and sharp. The 

 molars are five above and four below on each side, short, and the crown 

 tuberculous. The species are all of small size, and longitudinally striped on 

 the back and sides. They do not mount trees unless driven thither by 

 necessity, but dig burrows, and spend their nights and the season of winter 

 under the ground. 



Several species of this genus exist in North America ; one is known in 

 South America, and another in the northern portions of the eastern con- 

 tinent. The chipping squirrel or hackee {Tamias lysteri) is found from 

 the northern lakes (Huron and Superior) all along the eastern, northern, 

 and middle states and range of Alleghany Mountains. 



The genus Sciurus is characterized by an elongated body ; a long tail, 

 67 1 



