Zoological Society. 129 



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

 sufficient ground to separate generically the two species if they were 

 unaccompanied by modifications of other parts of the 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 tuberculate 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, is 

 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 which 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- 

 molaresg^; molares j^: =40; ^tq 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 

 character, with the modification of the tail, induced M. Desmarestto 

 separate the Pigmy Petaurist from the rest of the species, and con- 

 stitute a new subgenus under the name of Acrohata. 



In four adult specimens, and two of which had young in the pouch, 

 I find the'following dental formula to be constant ; — incisors ^ ; ca- 

 nines — y; prsemolares ~; molares |^: =36. 



The three quadricuspidate grinders of the upper jaw are preceded by 

 three large spurious molares, each of which has two fangs, and a com- 

 pressed, triangular, sharp-pointed crown, slightly but progressively 

 increasing in length, as they are placed forwards. An interspace 

 occurs between these and the canine, which is long, slender, sharp- 

 pointed, and recurved. The first incisor is longer than the two be- 



