PROFESSOR OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 
279 
molar in each of these fossils indicated, however, a larger species. This molar, more- 
over, presented good differential characters in the presence of the well-defined, though 
small, postbasal ridge (ib. fig. 7, g ), the large prebasal ridge (ib. f), and the well- 
developed and almost equal-sized fore link (s) and mid link (r) ; the proportions of the 
two principal transverse lobes in the minor breadth of their outer and inner convex 
borders as compared with their' height were rather those of Sthenurus than of Macro - 
pus. But Sthenurus Atlas shows no postbasal ridge '(comp. Plate XXIV. fig. 15, 
Protemnodon Mimas, with the same view, Plate XXII. fig. 8, of the homologous tooth 
in Sthenurus). 
On the hypothesis that the specimens Plate XXIV. figs. 13-16 and Plate XXVI. figs. 
4 & 5 belonged to the same species as the specimen Plate XXVI. figs. 1 & 2, the last, 
largest and best-preserved unworn molar in the smaller jaws would be homologous with 
the antepenultimate and worn molar in the larger jaw. The test-scrutiny was accordingly 
applied, and the germ of the large premolar characteristic of the genus Protemnodon 
was brought to light in both the smaller fossils (Plate XXIV. fig. 14, p 3 , Plate XXVI. 
fig. &,pz). The Kangaroos leaving these remains had each perished at the same phase of 
dentition as that shown in the type specimen of Sthenurus Atlas (Plate XXII. figs. 3 & 4) ; 
the subgeneric characters afforded by the premolar are well exemplified thereby. The 
comparatively flat undivided outer surface, with the continuous straight trenchant margin 
of the crown of p 3 in Protemnodon, contrasts with the two convex lobes defined by the 
median fissure notching the trenchant margin and deeply grooving the outer surface of 
the crown of p z in Sthenurus ; and these differences are better marked in the originals 
than in the figures above cited, although these give the details with quite sufficient 
accuracy. 
The mandibular fossils of the young Protemnodon supply acceptable additional 
evidence of the dental characters of the species. Thus the crown of d 4 , which is 
mutilated in the type mandible (Plate XXVI. fig. 3), is entire in figs. 4 & 6, 
save as regards the degree of masticatory abrasion to which it has been subject, 
exposing a linear tract of dentine on each main lobe expanding where the link joins 
such lobe. The postbasal ridge (Plate XXIV. fig. 13, d i) is as conspicuous in this 
as in the succeeding tooth, m i ; the prebasal ridge shows also a proportionate 
development, with the fore link distinct (Plate XXVI. fig. 6, d i, s). The first 
and second deciduous molars (ib. di, dz) occupied an alveolar extent of 9 lines ; they 
were displaced, as usual, by the rise of the premolar with a crown of corresponding 
antero-posterior extent. The subject of figs. 13-15, Plate XXIV., was from a 
younger animal than that of figs. 4-6, Plate XXVI. ; in the former the molar (m i) 
had very recently risen into place ; in Plate XXVI. figs. 4-6 the enamelled 
summits of the transverse ridges of m i are a little worn, as usual, from above downward 
and backward. 
The socket of the incisor in the subject of fig. 4 is broken across about an inch 
from its closed end ; the fracture (ib. fig. 8, i) gives, therefore, the breadth and thick- 
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