PROFESSOR OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 
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(d 2, d 3) have been displaced by the rise of p 3 in the Oxford specimen of Sthenurus 
Atlas (Plate XXII. figs. 5-8) : one of these, viz. d 3, is retained in the type specimen 
(ib. figs. 3 & 4, d 3) . 
The molar following^ 3 in Plate XXII. figs. 5, 6, 8, answers to di in the placental 
diphyodont dentition* ; its crown differs from that of the younger (type) Sthenurus Atlas 
only in a slight superiority of size. The prebasal ridge is linked to near the middle of 
the front transverse lobe, a little nearer the outer side, making the worn surface there 
somewhat thicker ; the mid link rising from the middle of the base of the hind part of 
the front lobe rises to join the hind lobe at a similar position, and with a similar result 
to the grinding-surface. The more produced prebasal ridge of the next molar presses 
upon the back part of the hind transverse lobe of d 4, above the feeble outswelling 0 f 
the base of that tooth. The fore-and-aft extent of the prebasal ridge, with its linking 
bar inclining obliquely outward to abut upon the front transverse lobe, characterizes 
the three true molars, m 1, 2, 3. The transverse breadth of the hind lobe of m 3 is rather 
less than that of the front lobe. 
The molar series of the present mandible describes a feeble convexity outward. 
The figures in Plate XXII. being of the natural size precludes the need of recording- 
admeasurements. 
The subject of figs. 7 & 8, Plate XXIV., and of fig. 9, Plate XXII., is a portion of the 
left mandibular ramus (drawn in the Plate without reversing) of Sthenurus Atlas , from 
an older individual than that which afforded the more entire ramus, but retaining the 
four first molars and part of the socket of the fifth. 
The outer and posterior lobe of the premolar (Plate XXII. fig. 9 ,p 3, b) has been worn 
down below the level of the posterior part of the antero-internal lobe (Plate XXIV. figs. 
7 & 8, c ), which stands up as an angular trenchant ridge ; on the broader outer lobe a flat 
field of dentine is exposed, showing that the back part of this premolar, as in Nototherium, 
took some share in mastication, not merely in division of the food as in Halmaturus 
ualabatus ; so much of the grooves, ridges, and other accentuations of the crown of 
p 3 as remain in the present specimen repeat those characters in the unworn homologue 
of the two preceding specimens. 
The crown of d 4 (Plate XXII. fig. 9) shows a field of dentine enclosed by a border of 
enamel encroaching by a curved indent in opposite sides, and with a feeble fold at the 
outer part of what was the prebasal ridge. The dentine of this ridge is worn in m 1 
into continuity with that of the front lobe, and a small portion of the same tissue is 
exposed on the back lobe. In m 2 the enamelled summits of the transverse lobes are 
worn obliquely backward, the enamel showing there a finely polished tract. The basal 
swelling at the back part of this molar is better defined than in the type specimen ; 
in neither is the hind surface of the molars impressed as in Macropus Titan. The present 
specimen agrees in size with the comparable or homotypal parts of the upper jaw 
(Plate XXIV. figs. 4, 5, 6). The slight difference of size as compared with the mandible 
* Phil. Trans. 1870, p. 539, fig. 3 (Sus). 
2 N 2 
