MAMMALS THAT GNAW. 91 



the typical, or northern fly ing -squirrels, together with marmots, chipmunks, 

 etc. The family is distinguished from the last by the absence of scales on the 

 bushy tail, and the presence of postorbital processes defin- 

 ing the hinder border of the socket of the eye ; while if a Squirrel Tribe. 

 parachute is developed, it is supported by a cartilaginous Family 



rod arising from the wrist. The palate is broad, and there Sciuridcu. 

 are usually two pairs of upper and one of lower premolar 

 teeth, although the first pair in the upper jaw, which are always small, may 

 be shed at an early age, or even wanting. The cheek teeth are rooted, and 

 in the young always bear tubercles on their crowns, although in the adult 

 these may be converted into deep plates separated by clefts extending par- 

 tially across the crown. With the exception of Madagascar and Australasia, 

 the family has a cosmopolitan range. 



The first genus is represented only by the large groove-toothed squirrel 

 (Rhithrosciurus) of Borneo, easily recognised by the numerous vertical grooves 

 on the upper incisor teeth. Next come the Ethiopian spiny squirrels (Xerus\ 

 typically characterised by the coarse spiny fur, the small size or absence of 

 external ears, and the comparatively straight and long claws ; while they are 

 further distinguished by certain features of the skull and teeth. This group 

 ranges all over Africa from Abyssinia southwards. The numerous species of true 

 squirrels (Sciurus) differ from the last by the shortness of the skull, in which 

 the postorbital processes are more elongated. The tail is very long and bushy ; 

 the ears are generally large, and in some instances tufted ; there are only 

 four functional toes to the fore-feet ; the claws are long, curved, and sharp ; 

 and the females have either four or six teats. The cheek teeth have low 

 tuberculated crowns. The genus has a very wide distribution, but attains its 

 maximum development in the Malayan countries. Whereas, with the excep- 

 tion of the muzzle and chest, the common squirrel ($. wdgaris) is nearly 

 uniform brownish-red, the little Indian palm-squirrel (8. palmarum) is marked 

 with longitudinal dark and light stripes on the back, and many species have 

 two or three conspicuous bright-coloured and white bands oil the flanks, 

 while one American form is peculiar among Mammals in assuming a special 

 brilliant breedir.g-dress. A.11 the squirrels are arboreal, but their habits are 

 too well known to need special mention. From the true squirrels the 

 ground-squirrels, or chipmunks (Tamias), of the northern portions of both 

 hemispheres, differ by having pouches inside the cheeks for the storage 

 of food ; and are also characterised by the presence of distinct white or 

 greyish-white longitudinal stripes bordered by black bands on the sides, or 

 sides and back. Chipmunks, which are among the most common of North 

 American Rodents, are terrestrial in their habits, and chiefly remarkable 

 for the accumulations of food which they collect for winter use ; such 

 supplies being carried to the place of storage in the capacious check 

 pouches. 



The susliks, or gophers (Spermophihis *), which have a geographical distri- 

 bution nearly similar to that of the chipmunks, although most of them are 

 found in desert regions where the latter never go, are readily characterised 

 by their somewhat slender and squirrel-like form, the presence of cheek 

 pouches, and therudimental first toe of the fore-foot, which may, however, be 

 provided with a nail. In the skull the first upper premolar is larger than in 

 the true squirrels, and the two series of cheek teeth are nearly parallel. 

 The ears may be either minute, or relatively large and tufted ; and the tail 

 1 The earlier name Anisonyx is used by American authors. 



