786 
PROFESSOR OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 
I have seen none such in the corresponding part of any molar of Macrojpus Titan ; and 
it may be a variety in the individual specimen exemplifying or indicating the present 
subgenus. 
But the character of the back part of the molar is decisive, so far as my present 
observation of existing and extinct Kangaroos has extended, of the taxonomic distinction 
which I have assigned to Leptosiagon gracilis. 
§ 5. Genus Procoptodon *, Ow. — The indications of this genus, at first fragmentary, 
have been raised, by evidences successively received since the year 1845, to demonstra- 
tion, under, at least, three specific modifications. 
The first of these is exemplified, mainly, by maxillary fossils. The most instructive 
are portions of the right and left maxillary bones, each with three molars ( d 4, m i, m 2 ) 
and part of a fourth, d 3 (Plate LXXVII. figs. 2-6), of the same skull. 
In antero-posterior extent and in breadth the two molars (m 1 , m 2 ) do not exceed their 
homologues in the upper jaw of Sthenurus Brehusf ; but the configuration of the 
grinding-surface is different and much more complex, of itself indicating a distinct genus 
if not subfamily of Macrojgodidce. 
The prebasal ridge (f) is narrower than in Sthenurus ; it descends (the tooth being 
viewed prone) from the fore part of the outer angle of the front lobe (a) and then passes 
inward with a slighter descent to the fore part of the base of the inner half of the front 
lobe, subsiding before attaining the inner side of that lobe. The fore link (s) is feebly 
represented by a vertical ridge on the fore part of the front lobe, nearer its outer than 
inner end, the rest of that fore surface being marked by more minute vertical ridges 
and grooves. The hind surface of the front lobe is bounded by sharp subvertical ridges, 
respectively descending, with a slight degree of convergence, from the hind part of the 
outer and inner angles of the front lobe. In the transverse concavity of the hind 
surface of that lobe, so bounded, two stronger sharp vertical ridges of enamel descend 
toward the intervening valley, the outer ridge being continued backward across the 
valley as the 4 mid link’ (r), with a slightly sinuous course, convexly outward. The hind 
surface of the hind lobe (ib. fig. 5, m 2 ) almost repeats the characters of that of the front 
lobe ; the inner (g) of the two submedian vertical ridges in the concavity of such surface 
expands at its base into the convexity of that part of the molar ; the outer submedian 
ridge is minute. From the outer lateral or boundary-ridge a sharp vertical plate of 
enamel ( h ) is directed inward, and there are some minor sculpturings of this part of the 
hind surface. Its basal part is somewhat bulging and smooth, as are the outer and 
inner swollen ends of the two main transverse ridges or lobes (ib. fig. 6, a , h). 
The second molar ( m 2 ) is rather larger than the first ; both are feebly abraded along 
the fore part of the transverse summits of the wedge-shaped lobes, but not so far as to 
expose the dentine ; both teeth are behind the back surface of the masseteric process 
(ai«). These signs of immaturity were associated with and confirmed by the presence of 
* From irpd, before; (ccbrrw, to pound; ocovs, tooth, 
t Philosophical Transactions, 1874, Plate xxvir. fig. 6, mi, m 2 . 
