410 



vidua! of its kind. Sufficient of the bony palate remains to show (as in the younger 

 type specimen) that it was entire, as in Macropus proper and Osphranter. 



The interorbital aperture of the suborbital canal in Phascolagus is single, subcircular, 

 and well defined ; its fore and upper border rises upon a ridge or plate of bone, which 

 extends forward and outward to near where the masseteric ridge subsides into, or rises 

 from, the fore border of the orbit. This structure I have not observed in the skull of 

 any existing species of Macropus, Osphranter, or Halmaturus ; the nearest approach to 

 it is seen in the skull of Boriogale magnus. 



A second and larger proportion of the upper jaw of Phascolagus alius in the Ben- 

 nettian series shows, on the left side, the base part of the crown of the premolar in 

 place, and the sharp summits of the lobes of the last molar emerging from their 

 nursery. The antecedent molars show more wear than in the preceding specimen. 

 The mid-link in d 1, in the present, is worn down to the dentine ; yet the second lobe 

 of m 2 is less abraded, and the fore link is rather more conspicuous. 



On the right side the hind molar and its socket have been broken away. More of 

 the premolar is preserved, but the bilobate outer part of the crown is wanting ; it had, 

 plainly, the antero-posterior dimensions of the'entire crown exposed in the type specimen 

 (Flare LXXXII. fig. 1). The tract of the suborbital canal is exposed in both halves of 

 this upper jaw ; and we see that its anterior outlet must be far in advance of the orbit, 

 and about half an inch above the fore end of the premolar. 



The molar series in this fossil equal in extent and in the size of the teeth those of 

 Macropus rufus and Macropus major ; they rather exceed in size those in the younger, 

 perhaps female, individuals represented by the first-described fossil from the fresh- 

 water beds of Queensland and by the type specimen of Phascolagus alius. 



§ 7. Sthenurus Atlas. — Similar considerations to those which influenced judgment 

 and action in regard to the type fossil of Macropus Titan, added to plainer indications 

 of the incomplete development of the rear teeth of the molar series in the fragment 

 under scrutiny, led me, in 1837, to perform the same operation on the subject of fig. 4, 

 Plate LXXXII. * ; and great was my surprise at the result. 



The hidden germ (p s) equalled in antero-posterior diameter both the deciduous molars 

 which it would have displaced, and surpassed in that diameter the largest of the molars 

 to the extent of one half that length of their crown. For the great extinct species of 

 Kangaroo so indicated I proposed the name of Macropus Atlas f. 



The tooth so discovered recalled a dental characteristic of the Potoroos, or Kangaroo- 

 rats (Hypsyprymnus, &c) ; but the molars in the fossil were strictly bilophodont, more 

 so. indeed, than in Macropus Titan or the existing Macropus major. There was less 

 indication, for example, in the "links" of any subdivision or reduction of the two trans- 

 verse ridges to a quadrituberculate grinding-surface ; they stood out more definitely 

 and more freely. Moreover, the large premolar of the fossil was primarily divided exter- 

 nally into a fore lobe and hind lobe by a vertical fissure continued as a groove almost 

 * Plate xxix. fig. 1, Mitchell's 'Three Expeditions,' &c, vol. ii. 1838. t Ibid. p. 359. 



