270 
PROFESSOR OWEN ON THE EOSSIL MAMMALS OF AUSTRALIA. 
firmer junction of the rami, as well as in the characters oi p 3, the present genus offers 
a nearer approach than does Macropus proper. Moreover, as the socket of the incisor 
follows the direction of the symphysis, the tooth projects less horizontally than in 
Macropus, and rises at a similar angle with the horizontal lower border of the ramus*. 
In all the characters of the symphysial end of the mandible Halmaturus ualabatus 
(Plate XXIV. figs. 10, 12) agrees with Macropus and differs from Sthenurus. 
The lower border of the crown of the incisor, with the free end of that tooth, is 
broken away in the Oxford specimen, but enough of the crown remains to show that it 
is shorter but vertically broader than in Macropus proper. The enamel is confined 
to the under and outer sides ; the radical cement encroaches on the outer enamel in an 
angular form (Plate XXII. fig. 5, i). The upper border of the base of the crown is 
trenchant ; the tooth gradually gains in thickness to the lower border, but even here it 
is less than half the vertical breadth of the crown; the inner surface, behind the 
working one, is vertically more concave than in Macropus Titan. The hind part of the 
narrow surface of attrition upon the upper edge of the crown begins half an inch from 
the hind border of the enamel. 
The premolar with a fore-and-aft extent of crown of 8 lines (17 millims.), a vertical 
extent of 6 lines (12 millims.), and a greatest breadth, near the hind border, of 3 lines 
(6^ millims.), is, externally (ib. fig. 5, p 3), divided into two subequal lobes; but the 
vertical fissure runs obliquely backward and inward, so that the lobe forming the 
anterior half of the outer surface of the crown forms the whole of the inner surface. 
This lobe has a slight prebasal prominence, and is divided above by two vertical 
transverse fissures, the foremost of which is in view on the outer surface, extending 
nearly halfway down the crown ; this fissure widens to the upper border, where the two 
divisions of the lobe which it separates are linked by a slender longitudinal bar of 
enamel. The second transverse fissure is not so widened above, but the rudiment of an 
enamel link appears behind the second transverse division of this lobe ; the third 
division is less definitely cleft or marked off from the rest of the antero-internal lobe, 
which is continued with a trenchant border to the back part of the crown to which it 
descends; vertical depressions, hardly to be called fissures, are indicated on the inner 
surface of this hinder portion of the lobe (Plate XXII. fig. 6,p 3). The postero-external 
lobe (ib. fig. 5, p 3) has a simple trenchant edge, describing a slight convexity length- 
wise ; it is connected with the postinternal lobe by two transverse enamel links, the 
foremost being the largest (ib. fig. 8, p 3). 
The outer surface of this complex tooth (p 3) is shown in fig. 5, the inner surface in 
fig. 6, and the upper surface in fig. 8. The homologous tooth in Halmaturus ualaba- 
tus (Plate XXIV. figs. 10, 11, 12, p 3) shows nothing of the complexity answerable to 
that which renders the upper premolar of that Wallaby so similar to the upper premolar 
of Sthenurus ; it has an undivided trenchant crown, slightly thickened behind, with some 
veiy feeble indications of vertical grooving on both inner and outer sides. Two teeth 
* Compare fig. 6, Plate XXII. with fig. 4, Plate vi. Phil. Trans. 1872. 
