152 



Belideus, is much less than in Petaurus. In Belldeus the molars oc- 

 cupy a space equal to rather more than two-thirds of that between the 

 incisors and first true molar ; whereas in Petaurus, 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 Beli- 

 deus they decrease considerably from the first molar to the last. In 

 Petaurus, again, there are five molars on each side of the lower jaw 

 opposed to six in the upper jaw, all of which are fitted for the masti- 

 cation 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 com- 

 paratively large size of the canines, and the series of small teeth in 

 front of the molars, 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 somewhat suddenly descends in front of the 

 molars, and the coronoid process is comparatively broad. 



"Petaurus sciureus may be regarded as the type of the section Be- 

 lideus, which will also contain P . flaviventer and P. breviceps. 



" In the third section, which is the subgenus Acrobata of Des- 



marest, the incisors are g ; canines, ^^ ; false molars, ^^ ; true mo- 

 lars, 3:^=36. The incisors resemble those of Belideus; the canines 

 are well-developed, long, pointed, and recur\-ed, placed close to the 

 intermaxillary suture, and even encroaching slightly on the intermax- 

 illary bone. The three false molars of the upper jaw have each two 

 fangs, they are compressed, sharply pointed, and viewed laterally, of 

 a triangular form. The first and second are about equal in size, and 

 larger than the third, the apex of which projects beyond the level 

 of the crowns of the true molars. Between the first and second false 

 molars on each side there is a narrow space ; the third is placed 

 close to the true molars ; these as well as those of the under jaw 

 resemble the true molars of Belideus ; there is however one less on 

 each side of both jaws. The incisors of the lower jaw also resemble 

 those in Belideus. Behind these incisors there are two minute teeth 

 on each side, which are followed by two sharply pointed false molars, 

 the foremost of which is the larger, and the apex of the second is 

 raised above the plane of the true molars. 



" The difference in the form of the false molar teeth pointed out, 

 together with the reduced number of true molars, the slenderness 

 of the zygomatic arch, and the incurved angle of the lower jaw, 

 combined with the imperfect state of the palate, will serve to distin- 

 guish the species of the present section from the preceding. Exter- 

 nally, the P. pygmaus (which is the type of M. Desmarest's sub- 

 genus) may be distinguished by its distichous tail. 



Petaurus breviceps. P. cinerea, lined dorsali longitudinali 

 membrandque Uiterali supra nigrescentibus, hac ad latera albd s 

 corpore subttis sordide et pallide cinereo : caudd gracilis ad 

 apicem ftdiginosd ; auribu^ mediocribus, i 



