454 Zoological Sociely. 



responding pair above ; the enamel is confined to the anterior and 

 lateral surfaces of the crown ; but this, though beveled off from be- 

 hind forwards, terminates in a blunt apex by attrition against the 

 small middle incisors of the upper jaw ; the posterior surface of the 

 crown is impressed with a narrow longitudinal groove. These in- 

 cisors, like those above, are developed by a temporary pulp, and have 

 the fang contracted and solidified. In this respect the Koala re- 

 sembles the Pkula>igerSy and diflfei s from the Potoroos, which have 

 the fang of the large anterior incisors open for the reception of a 

 persistent pulp. In the compressed and sectorial structure of the 

 pramolares of the Koala, we perceive, however, an evident transition 

 to the characteristic form of these teeth in Hypsiprymnus ; but in 

 this genus the prcemolares are still more compressed^ and are remark- 

 able for their antero-posterior extent, which dimension becomes ex- 

 cessive in the arboreal Potoroos of New Guinea. 



So far, therefore, as the affinities of a Marsupial quadruped are 

 indicated by its teeth, the position assigned to the Koala by Latreille*, 

 viz, next to the Phalangers, must be regarded as more natural than 

 that which it occupies in the ' Rfegne Animal' of Cuvier, viz. between 

 the Kangaroos and Womhat. From the Kangaroos the Koala diiFers 

 in the presence of canines in the upper jaw ; and still more so from the 

 Wombat, which has neither canines nor posterior incisors ; whereas 

 the Koala not only closely resembles the Phalangers and Petaurists 

 in the correspondence as to number, kind, and conformation of its 

 teeth, as compared with the functionally developed teeth of those 

 geneni, but also agrees with them in the conformation of its di- 

 gestive organs, having a simple stomach, and a very long caecum. In 

 the Wombat, on the contrary, the caecum is short and wide, and has 

 a vermiform appendage. Both the Potoroos and Kangaroos differ 

 from the Koala and Phalangers in their large sacculated stomach 

 and relatively shorter caecum ; but the Potoroos, in the comparative 

 simplicity of this organ, as well as in the presence of superior canine 

 teeth, have clearly the nearer affinity to the Koala. Since, more- 

 over, the Petaurists have canines in both jaws like the Phalangers, 

 while the Koala possesses them only in the upper jaw, the place of 

 the Petaurists should be between the Phalangers and Koala, and 

 not, as in Latreille's system, between the Kangaroos and Potoroos ; 

 and Professor Owen proposed to include the Koala with the Pha- 

 langers and Petaurists in one subdivision, and to join the Potoroos 

 with the Kangaroos to form another and distinct primary group of 

 Marsupialia. 



* Families Nat. du Regne Anim. p, 53. 



