MARSUPIALS. 385 



and soft hairs, whilst in others, the hairs are arranged in two lateral 

 series. 



In the Petaurists, however, there is as little constancy in the 

 exact formula of the dentition as among the Phalangers. The largest 

 species of Petaurus {Pet. Taguanoides) , for example, is almost identical 

 in this respect with the Phalangista Cookii, which M. Fr. Cuvier 

 has therefore classed with the Petauri. Those teeth of Pet. Ta- 

 guanoides which are sufficiently developed and so equal in length 

 as to exercise the function of grinders, are six in number on each side 

 of the upper jaw, and five on each side of the lower jaw. The four 

 posterior molars in each row are true, and bear four pyramidal 

 cusps, excepting the last tooth in the upper jaw, which, as in 

 Ph. Cookii, has only three cusps. In the upper jaw the space 

 between the functional false molars and the incisors is occupied 

 by two simple rudimentary teeth, the anterior representing the 

 canine, but being relatively smaller than in Ph. Cookii ; the crowns 

 of the two anterior incisors are relatively larger. In the lower jaw 

 the sloping alveolar surface between the functional molars and 

 large procumbent incisor is occupied, according to M. Fr. Cuvier, by 

 two rudimentary minute teeth ; but I have not found any trace of 

 these in the two skulls of Pet. Tagua-noidts examined by me. 



In Petaurus sciureus and Petaurus Jlaviventer (PL 100, fig. 4) the 

 dentition more nearly resembles that of Phalangista vulpina. In 

 the upper jaw the functional molar series consists of five teeth on each 

 side ; the four hinder ones being, as in Pet. Taguanoides, true tuber- 

 culate molars, but diminishing more rapidly in size as they are placed 

 further back in the jaw ; the hinder tooth has three tubercles, the rest 

 four : the apices seem to be naturally blunter than in Pet. Taguanoides. 

 Between the functional premolar and the incisors there are three 

 teeth, of which the representative of the canine is relatively larger than 

 in the Pet. Taguanoides ; the second false molar is also larger and has 

 two parts ; the first, which is functional in Pet. Taguanoides, is here 

 very small. The first incisor is also relatively larger and more pro- 

 duced. In the lower jaw the functional series of grinders consists 

 of the four true tuberculate molars only, of which the last is 

 relatively smaller, and the first of a more triangular form than in 



c c 



