72 
PROFESSOR OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 
6 lines ancl 5 lines ; but the vertical diameter of the hollow base exceeds an inch, the 
length of the entire though incomplete tooth being 2 inches 9 lines. It is directed 
obliquely forward and upward, at an angle of 140°, with the lower border of the ramus; 
a rather less open one than in Diprotodon. 
The socket of the first molar (d s) begins in this young jaw one inch behind the opening 
of that of the incisive tooth, which gives the length of the diastema (ib. fig. 1, k ) at this 
stage of dentition. The first molar has an anterior and a posterior lobe. The front lobe 
is highest, and is a three-sided cone, with one angle in front and rather produced or ridge- 
like ; it is subcanaliculate internally : the two posterior angles are continued into the 
fore and hind borders of the hind lobe ; this is transverse, low, flat, inclined from behind 
forward and rather downward to the base of the front lobe. Both lobes are convex 
outwardly, and separated there by a shallow depression ; the inner side of the tooth is 
much lower than the outer one. The fore-and-aft diameter of the crown is 9 lines, the 
transverse diameter posteriorly 6| lines; it is implanted by two fangs (ib. fig. 5, l), one 
behind the other, and each 10 lines in length ; the entire length of the tooth, vertically, 
is 1 inch 6 lines. 
The second molar (ib. d 4) assumes the two transversely ridged or bilophodont type, 
the lobes being in the form of transverse wedges. The anterior lobe is narrower trans- 
versely, broader from before backward than the posterior one. The anterior basal ridge 
(f) is a continuation of the slightly produced fore margins of the outer and inner sides 
of the front lobe, at their lower ends, into one another, defining below the slightly exca- 
vated surface on the fore part of the anterior lobe, the enamel of which is finely rugous. 
From the junction of the basal with the outer vertical ridge, a similar ridge is continued 
curving downward and backward, and then rising upon the posterior part of the outer 
surface of the front lobe (ib. fig. 1, a), defining upon that surface a finely rugous tract of 
enamel. The inner side of the front lobe (ib. fig. 4, a) has no such ridge. The hind 
surface of this lobe is less definitely bounded by a backward prominence of the outer 
border, and a slight vertical ridge or fold of enamel near the inner border. The valley 
(A) between the lobes has both the outer and inner entry crossed by a short ridge, the 
outer one being the strongest. The posterior basal ridge (g) is the broadest ; its outer 
and inner ends bend up a short way upon the hind surface of the hind lobe. The line 
of initial abrasion at the edges of the two lobes is from above downward and backward. 
Both lobes present in profile a slight curve backward. The length (fore-and-aft dia- 
meter) of the tooth is 1 inch 2 lines; the breadth (transverse diameter) of the front 
lobe is 9 lines, that of the hind lobe is 11 lines. It is broader in proportion to its length 
than in Diprotodon*. The anterior and posterior basal ridges are narrower, relatively, 
than in that genus. 
The third molar (Plate VI., m 1) has the two lobes of equal breadth save at the sum- 
mit, where this dimension rather exceeds in the hind lobe ; the front lobe rises higher 
than the hind one. The front basal ridge is continued more abruptly from the anterior 
* Philosophical Transactions, topi. cit. Plate xi. figs. 2 & 3, d 4. 
