252 
PROFESSOR OWEN ON THE EOSSIL MAMMALS OF AUSTRALIA. 
but there is a smaller third tubercle on the inner side of the hind lobe, increasing the 
breadth of that part of the tooth, as was indicated by the last-described specimen 
(ib. fig. 10,^?3). The length of the entire series of five teeth is 2 inches 9 lines; that 
of the premolar (fore-and-aft diameter of crown) is 5 lines, that of the next tooth ( d 4 ) 
being the same ; that of the penultimate molar is 8 lines. The whole series is bounded 
on the inner side by an almost straight, very feebly concave line ; the outer contour is 
rather more convex. 
The two specimens above described are in the Museum of the Natural- History Society 
of Worcester, to the Council of which I am indebted for the opportunity of describing 
and figuring them. They were obtained by the donor, Henry Hughes, Esq., in the 
freshwater deposits of Darling Downs. 
The subject of figs. 15, 16, & 17, Plate XXI., is also from the freshwater deposits of 
Queensland. It includes a considerable proportion of the right maxillary, with the last 
four grinders in situ , the dentine being exposed along a very narrow strip of the front 
lobe of the hindmost tooth ( to 3). In the foremost ( d 4) the channel of dentine along 
the mid link is not quite exposed, the enamel at the base of the link still remaining. 
The two anterior deciduous molars and the premolar have been shed and the alveoli 
obliterated. This, therefore, is from a fully mature individual. The three teeth (d 4, m 1, 
to 2 ) homologous with the last three molars of the young specimen (ib. figs. 6-8) occupy 
the same longitudinal extent, viz. 1 inch 8^ lines : with the fully developed succeeding 
teeth they exemplify the later stage of the upper molar dentition in the present extinct 
species. The last molar (ib. figs. 15 & 16, to 3) shows well the characteristic modifications 
of its working-surface in Macropus Titan as compared with that in Sthenurus Atlas 
(Plate XXIV. fig. 6, to 3) : the prebasal ridge (f) is broader; its margin rises (the tooth 
being viewed prone) from the outer end to near the middle of its transverse course, then 
sinks more rapidly to its inner end, which bends up upon the front lobe. From the 
low or open angle thus described by the sharp margin of the prebasal ridge, the linking 
process (s) extends to near the middle of the fore part of the front lobe. In Sthenurus 
Atlas there is no front link ; the margin of the narrower and lower prebasal ridge forms 
no angle as it sinks to terminate at the fore and inner end of the front lobe. 
The mid link (Plate XXI. fig. 15, to 3, r) comes off from the front lobe nearer to its 
inner end in Macropus Titan, but not from that end as in Sthenurus Atlas (Plate XXIY. 
fig. 6, to 3, r). It is more developed in Macropus Titan , and its course is more longi- 
tudinal as it recedes to abut against the middle of the hind lobe; the postbasal 
ridge ( g ) extends from the postinternal angle of the hind lobe downward and outward 
to the postexternal part of the base of that lobe, leaving a well-marked oblique dent 
or cavity on the posterior surface of that lobe. In Sthenurus Atlas a general slight 
concavity of the hind surface of the hind lobe of to 3, upper jaw, is bounded 
below by a feeble postbasal ridge. With an equality of breadth, the fore-and-aft extent 
of the last molar in Macropus Titan exceeds that of Sthenurus Atlas by 1 line. 
The hind border of the front or maxillary pier of the zygomatic arch is on the vertical 
