PROFESSOR OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 
71 
basal ridges of the fourth have risen to the brim of the socket, the enamel shows only 
a linear trace of attrition on the ridges of the second molar (Plate VI. fig. 3, d 4 , h, with 
a very feeble trace on the anterior ridge of the third molar (ib. m i) ; its hind ridge and 
the crown of the first molar (ib. d s) are untouched. The inference is that the young 
Herbivore represented by the fossil derived a greater proportion of its nourishment from 
the mother, and much less from extraneous sources, than do the placental iierbivores 
at a corresponding stage of immaturity. 
In this respect the fossil repeats the molar conditions of a young Kangaroo ( Macropus ) 
at the same phase of dentition f. With this phase the existing marsupial herbivore has 
attained that size and strength as a denizen of the pouch in which it begins to protrude 
its head to crop, occasionally, a tender leaf or blade of grass while the mother may be 
browsing or grazing. In the singleness and size of the sloping incisor, in the shape and 
proportion of the first molar (d s), as well as in those of the second and third two-ridged 
grinders, d 4, & m 1, the fossil more closely resembles Macropus than any other known 
genus, whether marsupial or placental. 
I accordingly here pushed the comparative research a stage further, and removed the 
outer wall of the jaw, as in fig. 5, Plate VI., to see if the large Australian bilophodont 
fossil carried its correspondence with Macropus to the extent of showing the germ of a 
premolar ( p ; but of this tooth there was no trace. The length and deep implantation 
of the two fangs of d 3 (l), underlain by the expanded base of the procumbent incisor 
(ib. i *), make it very improbable that such germ of &p 3 could ever be developed in the 
species represented by the fossil. 
Thus the results of the above comparisons, independently of other evidences of Noto- 
therium , would have led to the conclusion that the young Herbivore, notwithstanding 
its bulk, belonged to a group of Mammals in which the milk-dentition was not so soon 
brought into use for grazing or browsing as in the Placental series ; that it, therefore, 
was probably a Marsupial ; which conclusion the close concordance in number and shape 
of grinding-teeth with the largest existing Herbivore of that order (the Kangaroo) 
would have put beyond doubt. 
The lower incisor, in the immature example, had pushed its tip, as has been said, 
about two thirds of an inch from the socket ; it is of a conical form, with an obtuse 
apex, which has been abraded for the extent of 3 lines (Plate VI. fig. 3, V). The enamel 
coats the outer and under part of the tooth, bending up a little way upon the flat inner 
side, and in an increasing degree as the tooth expands (Plate VI. fig. 4, e) : the enamel 
is not continued to the open base (ib. fig. 5, 7*) as in Diprotodon : the line of termina- 
tion is well defined. A thin layer of cement coats the rest of the tooth’s circumference. 
The fracture of the exposed crown of the tooth gives a subquadrate surface, longest 
vertically, with the lower and outer angle rounded off. The two diameters are here 
t Owen-, Art. “Teeth,” Cyclopaedia of Anatomy &c., fig. 594, B ; and ‘Anatomy of Vertebrates,’ vol. iii. 
fig. 296, B. 
t Philosophical Transactions, 1870, p. 539, fig. 4, p s. 
