264 
PEOFESSOE OWEN ON THE FOSSIL MAMMALS OF AUSTEALIA. 
lagus the prebasal ridge is larger than in Boriogale ; the breadth of the outer sides of the 
two main lobes is greater ; the postbasal ridge better defines the hinder depression below. 
Both the cranial and dental characters of Phascolagus forbid its reference to a Boriogale. 
In the upper molars of Osphranter , with a prebasal ridge developed in the same degree 
as in Phascolagus , the fore link is also present, though feeble ; yet in a more conspicuous 
degree than in Phascolagus , where it can hardly be said to exist : the fore link is better 
developed in the upper molars of Macropus major , and the valley is wider between the 
two lobes. 
The remains of the alveolar cavities for the two roots of the premolar show that it 
had come into place in the fossil under review ; and the fore-and-aft extent which the 
two cavities occupy with the width of the intervening tract of bone indicate a premolar 
about the size, in that dimension, of that of the type specimen (Plate XXII. fig. 1, p 3), 
and rather longer than the following tooth ( d 4), but far short of the proportions which 
characterize p 3 in the genera Sthenurus and Protemnodon, next to be defined. The 
state of the socket of m 3 in the Bennettian specimen, and the rising of its base between the 
insertions of the fore and hind fangs, clearly bespeak that this tooth had likewise 
come into place, and that the fossil under comparison is from a nearly mature indi- 
vidual 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 altus 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 4, 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 speci- 
men (Plate XXII. 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 altus. 
