PROFESSOR OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 69 
In not any of the upper molars is the anterior basal ridge (/) so large relatively 
as in Diprotodon. 
In the upper jaw of Not other mm Mitchelli, in which the last molar had recently 
come into place and the enamel had been slightly worn along the summit of the 
anterior ridge, the second molar showed the lobes worn down two thirds of the way 
toward the valley. In the cast of the right maxilla with the dentine exposed on the 
lobes of m 3, those of d 4 are worn down to the shallowest part of the valley. In the 
oldest specimen of this species the grinding-surface of this tooth (ib. fig. 7, d 4 ) is 
reduced to a smooth field of dentine ( d ) and osteodentine ( 0 ), with a peripheral boundary 
of enamel, e. This dental constituent does not exceed a line in thickness at this stage 
of abrasion. 
The dentition of the upper jaw of Not other ium inerme is known to me by a portion 
of that jaw with the right and left series of grinders and much of the intervening bony 
palate ; but the premaxillaries and upper incisors are wanting, being broken away with 
the contiguous part of the maxillary close to the molar (d 3) ; and both this and the 
second molar (d 4) are mutilated on the left side of the jaw. The right series is repre- 
sented of the natural size in figure 5, Plate IX. 
The first molar is relatively smaller and less complex on the grinding-surface than is 
d 3 in Nototherium Mitchelli (ib. fig. 4) : the transverse and antero-posterior diameters 
are alike. The outer lobe or division has one coronal prominence upon which a slender 
triangular tract of dentine is exposed extended antero-posteriorly ; a more equal-sided 
triangular tract is exposed on the shorter inner lobe ; an anterior and a posterior basal 
ridge bound corresponding depressions divided by the confluence of the apices of the 
outer and inner divisions at the centre of the crown ; a short external basal ridge closes 
the concavity impressed upon the hind half of the outer surface of the crown. One 
cannot distinguish, with certainty, the worn enamel from the dentinal tracts in the 
plaster cast of the answerable tooth of Nototherium Mitchelli ; nor do the photographs 
help in this particular ; but both concur in demonstrating the differences of size, shape, 
and proportion of the anterior molar, which I judge to exceed those allowed to sexual 
or individual variation, without affording ground for inferring generic distinction from 
the modifications of d 3, represented in Plate IX. 
The more constant teeth (d \-m 3) in figure 5 exemplify the Nototherian characters 
with the inferiority of size, corresponding with the little that is known of the present 
species. Nototherium inerme , like Not. Mitchelli , has the hind lobe of the last molar 
contracted in breadth, and the antero-posterior extent of the crown is less than that in 
the opposing molar (ms) of the lower jaw. 
A greater proportion of the enamel of this worn grinder, in the subject of fig. 5, 
Plate IX., shows the punctate rugous character than in the antecedent teeth. 
The specific character of Nototherium inerme is well exemplified by the minor rela- 
tive size of the anterior molar, d 3 (Plate IX. fig. 5), of the upper jaw, as by that of the 
incisor in the lower jaw. 
