48 Zoological Society. 



following species : — P. taguanoides, P, flaviventer, P. sciureus, and 

 P. pt/gmaus, and one skull of a new species hereafter described. 



*' In these crania three distinct modifications in the dentition are 

 observable ; and as they are combined with certain differences in the 

 skulls and in the external characters of the animals to which they be- 

 long, they may be regarded as forming three subordinate sections, to 

 which for convenience I shall apply the names, Petaurus, Belideus, and 

 Acrobata. Two of these names will be found in the * Mammologie,* 

 by M. Desmarest. The dentition observable in the species of 

 the first of these sections {Petaurus) is as follows: — Incisors-?; 

 canines q—qI false molars yzti ; true molars 53:5. I am induced to 

 call the two first teeth following the incisors canines, since they re- 

 present those which are evidently canines in the two next sections. 

 The incisors of the upper jaw are arranged laterally, the three on 

 either side being placed close together ; the two foremost are sepa- 

 rated from one another by a space about equal to their diameter ; 

 they are narrow at the base, and expanded and somewhat compressed 

 above the base. The next incisor on each side is larger than the 

 last or posterior one, and about half the height of the first, narrow 

 at the base, and wide and truncated at the apex. The third incisor 

 is small and but slightly wider at the tip than at the base. The 

 canine is very small, being in size about equal to the posterior inci- 

 sor ; its tip is rounded, and it springs from the maxilla a little behind 

 the intermaxillary suture ; the space between it and the canine being 

 about equal to twice its diameter or more ; for there is a difference in 

 this respect in the specimens before me. The first false molar is 

 minute and conical, separated by a considerable space from the 

 canine and also from the following molars. The next two molars 

 on each side I have called false molars, because they do not possess 

 the inner tubercles which are observed in those behind ; they are broad 

 at the base and compressed at the tip ; the foremost presents an an- 

 terior larger, and a posterior small compressed tubercle ; the third is 

 divided at the tip into three compressed points. The true molars are 

 nearly square, but rather longer than broad ; the crowm of each, with 

 the exception of the last, presents four tubercles, with sharp cutting 

 edges, and very much resemble those of a Ruminant animal. In the 

 last molar there are but three of these tubercles, two in front and one 

 behind. The incisors of the lower jaw are large, nearly cylindrical 

 at the base ; beyond this they are somewhat dilated, flattened, 

 pointed, and have two sharp edges. There are no minute detached 

 false molars in the lower jaw. The single false molar on each side 

 is placed close to the true molars, compressed in front and expanded 



