276 
PROFESSOR OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 
from the fore part of the outer swelling of the front lobe. The inner alveolar border 
(Plate XXV. fig. 8) runs from the postalveolar ridge ( t ) with a feeble concavity to m 1 , 
and then takes as feeble a convex course to the diastema (l). 
The subject of figs. 1 & 2, Plate XXV., was obtained by Henry Hughes, Esq., from the 
freshwater deposits exposed in the beds of creeks in Darling Downs. It is now in the 
Museum of the Natural-History Society of Worcester, to the Council of which Society 
I was indebted in 1858 for the permission to take the above description and figures of 
this instructive and, at that time, unique fossil. 
To Sir Daniel Cooper, Bart., I have since been indebted for the opportunity of 
describing and figuring a larger proportion of the left mandibular ramus of the same 
species of Protemnodon, with the molar series at nearly the same stage of attrition. It 
was discovered by Ed. S. Hill, Esq., in the freshwater deposits of Eton Vale, Queensland. 
Of this fossil I give an external view (Plate XXV. fig. 3), in which it will be observed 
that, as in the foregoing example, the crown of m i is more worn (has borne more of 
the work of mastication) than that of the antecedent molar (^ 4 ). I have noted the 
same circumstance in a Macropus major of similar age. This may not relate to an 
earlier period of m 1 coming into the line of work than the molar which precedes it, but 
more probably is due to the greater degree of pressure upon a tooth nearer the centre 
of motion of the mandible. The last molar (ib. figs. 3 & 4, m 3) shows the narrower 
hind lobe (b ) : the seemingly broader prebasal ridge (f) than in m 2 may relate to the 
less amount of attrition in m 3. The links are low and ill-defined in this, as in the type 
specimen. There is a slight bulge behind, but no indent marking a postbasal ridge in 
the hindmost molar. The inner vertical plate of the horizontal ramus is continued 
further back than in existing Kangaroos and Wallabies, forming an inner wall (ib. 
fig. 8, t), with a definite and sharp margin, beneath the base of the coronoid process ; 
and from the point where this hind margin of the inner mandibular plate is continued 
upward into the coronoid, a low ridge extends on the side of the plate next the large 
cavity of the ascending ramus forward and downward to the entry of the dental canal. 
This ridge (Plate XXV. fig. 14, g) divides the cavity into an upper ( f) and lower (a) 
compartment. The structure is repeated, as will be seen, in the specimen next to be 
described. 
The curve and direction of so much of the diastemal ridge (ib. fig. 3, l ) as is here 
preserved resemble rather that of Macropus and Halmaturus than of Sthenurus ; but 
the less mutilated specimen (ib. figs. 7 & 8) shows the toothless tract (/, s') to be rela- 
tively shorter as compared with the molar series than in either of those genera of 
existing Kangaroos. 
This specimen likewise forms part of the series of fossils from the river-beds at Eton 
Vale, Darling Downs, presented by Sir Daniel Cooper, Bart., to the British Museum. 
The molar series (Plate XXV. figs. 7, 8, 9 ,p z-m 3) agrees in extent and in the propor- 
tions of the five teeth with the type specimen, but the fossil is from a less aged individual. 
The hind angle of the sectorial crown of p 3 (fig. 9) is made obtuse and polished by wear. 
