198 
PROFESSOR OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 
mandible extends from the back to the front of the molar series is a character of the 
lower jaw of Macropus *, which contrasts with the uniformity of depth in that of 
Sthenurus f and Protemnodon$. 
The socket of the premolar (ib. fig. 5, p 3) shows the two roots of that tooth to have 
been simple ; the hinder one, in section circular, with a diameter of 3 lines, was larger 
than the fore root, which was compressed and elliptic in section. The fore-and-aft 
length of the crown of this tooth is indicated to have been between 8 and 9 lines. 
This accords with the same admeasurement of the upper premolar (p 3) of the fossil 
from another and remote locality, figured in plate lxxxii. of the Phil. Trans, tom. cit. 
The fore root of the next molar in the mandibular fossil from Darling Downs 
(Plate 19. fig. 5, d 4) is transversely elliptic, 5 lines in long diameter, with a mid groove 
along its hind surface. The hind root, with a larger and deeper longitudinal groove 
on its fore surface, is also transversely elliptical, with a long diameter of 6^ lines. The 
crown of this tooth, preserved in the right ramus (ib. figs. 1 & 2, d 4), shows a low, short 
prebasal ridge (/'), upon which the exposed dentine is continuous with that of the 
much-worn surface of the fore lobe (a), indicative of a linked connexion therewith. 
Along the mid link ( r ), also, a linear tract of dentine extends to the hind lobe (b). 
The postbasal ridge is feebly indicated at this stage of wear by a narrow fold of enamel, 
which extends from the dentinal tract at the back of the grinding-surface of the hind 
lobe, downward and outward to near the base of the crown. The fore-and-aft diameter 
of d 4 is 10-J lines (23 millims.), the transverse diameter of the hind lobe is lines 
(15 millims.). 
The chief difference in size of d 4 in the upper jaw§ is in the greater proportional 
breadth of the crown — a characteristic of the upper molars in Macropodidce : so much 
as remains of the prebasal ridge and of the two main lobes in the maxillary tooth 
conforms to the character of the mandibular homotype. 
The third molar (m 1) is well preserved in both rami of the present lower jaw. A 
continuous tract of dentine is exposed, by wear, from the fore lobe along the mid link 
to the postbasal ridge (g). The prebasal ridge is limited to the inner half of the fore 
surface of the fore lobe, where, also, it is alone visible in m 1 of the upper jaw. The 
postbasal ridge (< g ) is more developed on the inner side of the hind link, where it is 
divided from the hind lobe by a fossa ; on the outer side of the link the ridge rapidly 
sinks and subsides near the base of the crown ; the mid part of the postbasal ridge is 
half an inch above the basal line of the enamel (fig. 8, g). The main valley expands 
as it descends from each side of the mid link (r), and is closed by a low bar on both 
the outer (ib. fig. 6, v) and inner (ib. fig. 7, v') sides of the tooth. The fore-and-aft 
extent of the mandibular tooth (mi) is 1 inch, as in its homotype of the upper jaw; 
the transverse diameter of the hind lobe is 8 lines, in the upper tooth 9 lines. 
The less-worn crown of m2 shows more of the true pattern of the grinding-surface 
* See Phil. Trans. 1874, plate xxii. figs. 13, 15. 
t Ibid. figs. 5, 6. 
J Tom. cit. plate xxv. figs. 7, 8. 
§ Tom. cit. plate lxxxii. fig. 1, d 4. 
