THE BEAVER 467 



The caecum is disposed in a spiral. The teats are three pairs, 

 non-inguinal in position. 



The size of these squirrels is 16 to 18 inches exclusive of 

 the tail, which is longer. These animals can make an exceedingly 

 long jump with the help of their flying membrane. Nearly eighty 

 yards is the longest distance given for these aerial excursions. It 

 is stated that they are able to steer themselves to some extent 

 while in the air. As appears to be the case with so many 

 Eodents, these animals feed largely upon beetles and other insects, 

 besides bark, nuts, etc. 



The allied genus Sciuropterus has a much wider range. It 

 extends into the Palaearctic region and into North America, 

 besides being found in India. There is here no membrane reach- 

 ing to the tail. The palms and soles are furry. The caecum is 

 very much shorter, and so is the large intestine. The latter, in 

 X volacella, is not more than one-third of the length of the small 

 intestine. In other features there are no remarkable differences 

 in structure, save that the mammae, always three pairs, may be 

 inguinal. 



Of the genus Ewpctaurus^ but a single species is known, which 

 is limited to high altitudes at Gilgit and perhaps in Thibet. Its 

 principal difference from the other genera of Flying S(juirrels is that 

 the molars are hypselodont instead of brachyodont. The inter- 

 femoral membrane is rudimentary or \Mxnting. The one species 

 is E. cinereus. It is thought to live " on rocks, perhaps among 

 precipices." Dr. Tullberg attributes the hypselodont teeth to the 

 fact that the mosses upon which it is believed to feed may have 

 much sand and earth intermingled, which would naturally lead to 

 a more rapid wearing away of the teeth, and hence a need for a 

 good supply of dental tissue to meet this destruction. 



Fam. 3. Castoridae. — This, the third family of the Sciuro- 

 morpha, contains but one genus. Castor, the Beaver, with at most 

 two species, one North American, the other European. This large 

 Eodent has small eyes and ears, as befits an aquatic animal, and the 

 tail is exceedingly broad and covered with scales ; the transverse 

 processes of the caudal vertebrae, in order better to support the 

 thick tissues lying outside them, are divided in the middle of 

 the series into two. The hind-feet are much larger than the fore- 

 feet, and are more webbed than in any other aquatic Eodent. 



' Thomas, J. Asiat. Soc. Bengal, Ivii. 1888, p. 256. 



