50 Zoological Society. 



front, and consists chiefly of one triangular and pointed tubercle. 

 The first true molar on each side is considerably larger than the fol- 

 lowing molars, each of which is smaller than the preceding, so that 

 the last is not equal in bulk to one half of the first. With the ex- 

 ception of the last, all the true molars possess four somewhat blunt 

 and rounded tubercles, and in general appearance very much resem- 

 ble the corresponding teeth of a Squirrel. The last molar has but 

 three tubercles, two in front and one behind. 



" The incisors of the lower jaw are long, compressed, and pointed, 

 and have the upper and lower edges sharp ; they are almost horizon- 

 tal in their direction, being but slightly curved upwards. Next 

 follows a series of four small teeth on each side, which I have called 

 false molars, though possibly the last only is properly so called, that 

 having two fangs, whereas the others appear to have but one. The 

 true molars nearly resemble those of the upper jaw, though they 

 are narrower and longer. The first has a large irregular anterior 

 lobe, which is higher than the posterior portion of the tooth, which 

 is divided into two tubercles. The three posterior molars have each 

 four tubercles. 



" Besides the points of distinction already alluded to between the 

 species of the present section and the preceding, there are other 

 characters which cannot 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 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. 



