246 REMARKS ON POST-TERTIARY PHASCOLOMYID.E. 



The tibia, like the humerus, is unusually thin and angular. It 

 its within two millimetres of the same length as that of platyrhinus^ 

 but in general form it most resembles that of latifrons, the curve 

 of the shaft and more especially the dilatation of its anterior edge 

 between the proximal and middle thirds being rather pronounced. 

 The concave area beneath the popliteal notch is deeply excavated. 

 The proximal end of the hinder side of the shaft is broader, the 

 distal end of this surface narrower than in platyrhinus and its 

 edges are sharper, as, indeed, are most of the edges of the bone. 

 The distal articulation is reniform in shape, not, as usual, rhom- 

 boid ; the articulating surface for the astragalus is elongated 

 posteriorly, and is more distinct from the shaft than in platy- 

 rhinus ; the inner malleolus is longer, and its scaphoid facet com- 

 paratively small. In short, a wombat tibia could hardly present 

 more specific differences from the tibias of mitchelli and platy- 

 rhinus than does this bone. 



We have thus two species of PJiascolomys of co-equal size repre- 

 sented by limb bones as well as dental remains from the Darling 

 Downs. Not one of these bones can, without violence to common 

 sense, be identified with bones of platyrhinus. It would be absurd 

 to deny that any of them belong to the common species of the 

 period, P. mitchelli. The inference is irresistible that P. mitchelli 

 and P. platyrhinus are distinct species. 



It is a conclusion which is supported by a fine series of mandibles 

 of P. mitchelli in the Queensland collection. 



