1902.] ADAPTATIONS IN DIPROTODONT MARSUPIALS. 27 



and situation behind the first pair remind one of those of the 

 duplicidentate I'odents. The incisors in this animal serve thus to 

 nip oif pieces of the leaves. In Fsetcclochirus the lower incisors 

 are broad and have sharp cutting- edges also on the sides. They 

 therefore work together with the upper incisors as a pair of 

 scissors cutting off pieces of plants and leaves. Both halves of the 

 mandible are in this animal movable, wherfeby the cutting-power 

 of the lower incisors becomes more effective. They may thus 

 be compared in shape and in action with those of the Kangaroos. 



In Trickostorus the incisors are intermediate in shape between 

 those of the two animals just refei'red to. They are broader 

 than in the Koala, but have a cutting-edge only in front. In two 

 skulls of this animal before me it is plain that the lower incisors, 

 Avhen used, are able to work against all thi'ee pairs of upper 

 incisors, which are all worn — the median ones, however, in such 

 a manner that a sharp edge is left in front. The two halves of 

 the mandible do not seem to be movable. 



The subselenodont type of the molars is not so prominent in 

 this animal — at least not when the teeth are worn. The shape 

 and position of the molars seem also to be different in Tricho- 

 sicrits, because, at least in the specimens before me, the surface of 

 the two anterior upper molars slopes inwards and that of the 

 two posterior ones outwards. In the loAver jaw, in correspondence 

 herewith, the two anterior molars slope outwards and the two 

 posterior ones inwards. The crown of the posterior premolar in 

 each jaw slopes in the same direction as the anterior molars of 

 the same series close to which it is situated. In consequence of 

 this arrangement, the upper premolar and the anterior upper 

 molars effect the gliding in a median direction of the lower jaw 

 when both jaws are pressed against each other in the manner 

 described aloove ; but the posterior upper molars arrest the lower 

 jaw and hinder it from gliding further than to its normal 

 position. In connection herewith is also to be observed that the 

 mandibular molar series of Trichosurus — thus differing from the 

 Koala and Pseudochirus — have not a shorter distance inter se along 

 their whole length than the maxillary molar series. In Tricho- 

 siorits the molar series of both jaws are, posteriorly, almost 

 opposite each other, and only anteriorly have the mandibiUar 

 molars a more median position than the upper molars. This 

 accounts for the different direction of the anterior and posterior 

 molars. 



The teeth of a young Phalanger differ a great deal from those 

 of the old one of the same species. In the half-grown animal 

 the lower incisors appear to be absolutely broader than in the 

 adult. This is, however, only apparently the case. The breadth 

 is about the same in both. The incisors of the young are thus 

 not only comparatively broader, but their shape is also different. 

 They are much more flattened than in the adult and have sharjD 

 lateral edges, so that they resemble the coi'responding teeth of 

 PseiidochAras desci-ibed above, or of a Kangaroo. The I'esem- 



