14 



formula of the dentition as among the Phalangers. The largest 

 species of Petaurus, Pet. TagitanoUles, e. g., is almost identical in 

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

 therefore classed with the Petauri. Those teeth of Pet. Taguanoides, 

 which are sufficiently developed, and so equal in length, as to exercise 

 the function of grinders, or in other words, the functional series of 

 niolares, include six teeth on each side of the upper jaw, and five 

 teeth on each side of the lower jaw. The four posterior molares in 

 each row are true, and bear four pyramidal cusps, excepting the last 

 tooth in the upper jaw, which, as in Phal. Cookii, has only three 

 cusps. In the upper jaw, the space between the functional false 

 molares and the incisors is occupied by two simple rudimentary teeth, 

 the anterior representing the canine, but being relatively smaller 

 than in Phal. Cookii. The crowns of the two anterior incisors are 

 relatively larger. In the lower jaw the sloping alveolar surface be- 

 tween the functional molares and large procumbent incisors is occu- 

 pied, according to M. Fr. Cuvier, by two rudimentary minute teeth : 

 I have not found any trace of these in the two skulls of Pet. Ta- 

 guanoides examined by me. In Phal. Cookii there are three minute 

 teeth in the corresponding space, but these differences would not be 

 sufficient grouud to separate generically the two species if they were 

 unaccompanied b}' modifications of other parts of th; body. In 

 Petaurus sciureus and Petaurus flaviventer the dentition more nearly 

 resembles that of Phalangista vulpina. In the upper jaw the func- 

 tional molar series consists of five teeth on each side, the four hinder 

 ones being, as in Pet. Taguanoides, true tubcrculate molares, but di- 

 minishing more rapidly in size, as they are placed further back in the 

 jaw : the hinder tooth has three tubercles, the rest four ; their apices 

 seem to be naturally blunter than in Pet. Taguanoides. Between 

 the functional false molar and the incisors there are three teeth, of 

 which the representative of the canine is relatively much larger than 

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

 two roots ; the second, which is functional in Pet. Taguanoides, ia 

 here very small ; the first incisor is relatively larger and is more pro- 

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

 of the four true tuberculate molares only, of which the last is rela- 

 tively smaller, and the first of a more triangular form than in Pet. 

 Taguanoides. The space between the tuberculate molares and the 

 procumbent incisor is occupied by four small teeth, of w'hich the one 

 immediately anterior to the molares has two roots, the remaining 

 three are rudimentary and have a single fang. Among the species 

 exhibiting this dental formula, viz., incisors ?^ ; canines J^ ; prse- 

 molares g:^^; molares ^^: =40: are Pet. sciureus. Pet. flaviventer, 

 and Pet. macrurus. 



The Pigmy Petaurist differs from the preceding and larger species 

 in having the hairs of the tail distichous or arranged in two lateral 

 series like the barbs of a feather ; and in having the spurious molares 

 large and sharply pointed; and the true molares bristled each with four 

 acute cusps. This tendency in the dentition to the insectivorous 



