PHALANGISTID^E. 257 



be considered unimportant. The space occupied by 

 the grinding teeth of the upper jaw, compared with 

 the space between the last incisor and the first true 

 molar in the species of Belideus, is much less than in 

 Petaurus. In Belideus the molars occupy a space 

 equal to rather more than two-thirds of that between 

 the incisors and first true molar; whereas, in Petau- 

 rus, the four last molars occupy more space than 

 that which extends from them to the incisors. There 

 is a corresponding difference in the lower, jaw. In 

 Petaurus the molars are very nearly equal in size, 

 whereas in Belideus, they decrease considerably from 

 the first molar to the last. In Petaurus, again, there 

 are five molars on each side of the lower jaw oppos- 

 ed to six in the upper jaw, all of which are fitted for 

 the mastication of the food ; whilst in Belideus the 

 molar corresponding to the first on either side of each 

 jaw in Petaurus is so small, and its crown is so low 

 that it cannot be used in mastication. The compara- 

 tively large size of the canines, and the series of small 

 teeth in front of the molars, (which I always find 

 present,) will also serve to distinguish the species of 

 the present section from the preceding, where the 

 upper margin of the ramus of the lower jaw some- 

 what suddenly descends in front of the molars, and 

 the coronoid process is comparatively broad. 



Petaurus sciureus may be regarded as the type of 

 this section, which also contains P. flaviventer and 

 P. breviceps. 



In the third section, which is the subgenus Aero- 

 bata of Desmarest, the incisors are | ; canines, : ; 



