532 
PBOFESSOB OWEN ON THE FOSSIL MAMMALS OF AUSTBALIA. 
A cursory comparison of the two foregoing specimens suggests that in 1 (fig. 3, Plate 
XXXVII.) may have been destined to be pushed out by a vertical successor, which, in 
place in the larger specimen (m 1, fig. 2, Plate XXXVIII.), shows of course a less degree of 
abrasion. But this is not the case. I have in vain sought for evidence of any premolar, 
in either upper or lower dental series of Biprotodon : it differs from Macropus and resem- 
bles Phascolomys in this particular. All the teeth, like the last three grinders in the 
type diphyodont dentition, belong to the first set. The variety as to degree of attrition 
in molars of the same series is due to some modified habit of mastication : the difference 
in respect of size I ascribe to sex, the smaller grinders belonging to the female, con- 
comitantly with a general inferiority of bulk, as is seen in Macropus. The following 
admeasurements exemplify the difference of size in molar teeth, which is probably 
sexual : — 
Diprotodon. 
r 
Male. 
b 
Female. 
in. 
lines. 
in. 
lines. 
in 3. Antero-posterior diameter 
1 
10 
1 
7 
Transverse posterior diameter (base of front lobe) . 
1 
11 
1 
6 
in 4. Antero-posterior diameter 
2 
3 
9 
Li 
0 
Transverse posterior diameter 
2 
0 
1 
7 
in 5. Antero-posterior diameter 
9 
Li 
4 
2 
1 
Transverse posterior diameter 
9 
Li 
0 
1 
71 
1 2 
Antero-posterior extent of in 3, in 4, in 5 . . . 
6 
0 
5 
10 
The forms and proportions in which the four constituents of the molar teeth of Dipn 
toclon are combined, are exemplified, in the vertical longitudinal section of the last three 
upper grinders, in Plate XLII. fig. 1. The enamel (e) gains thickness as it recedes 
to a certain extent from the summits of the lobes, giving more resistance or grinding- 
power as the tooth wears down ; but the enamel thins again at the base of the lobe ; it 
gains a little more thickness as it is reflected, so to speak, over the basal ridges, beyond 
which it extends from three to four lines before thinning off, and ceases upon the body 
of the tooth before its division into fangs. The usual general direction of the dentinal 
tubules is well displayed, as in most fossil teeth. As the dentine becomes exposed and 
abraded, the pulp-cavity is defended by the coarser calcification of the remaining matrix 
near the field of abrasion, and from 2 to 3 lines of osteo-dentine is interposed between 
that field and the pulp-cavity. In each lobe of the tooth most worn (m 1) the cavity is 
reduced to a linear trace. In the anterior lobe of in 2 it is more expanded ; and it 
retains width in both lobes of m 3. In each tooth the pulp-cavity has received a 
lining of dark-coloured spar in the course of fossilization. The cement is thickest upon 
the back part of the hind root ( c ), whence it extends upon the posterior basal ridge : 
this partial excess of cemental development assumes a characteristically definite figure 
in such sections as the one described. 
The lower incisors (Plates XXXV., XLI. & XLII. i\ Plate XXXIX. figs. 4, 5, 6 ) are 
