100 
They vary in size, the length antero-posteriorly ranging from 
22 m/m to 20 in/m, and the width from 20 m/rn to 23 m/m. The 
tooth is markedly tuberculate, consisting essentially of three external 
and two internal tubercles or cusps. The anterior external cusp 
occupies a talon projecting from the main mass of the crown and 
may be connected with the succeeding external tubercle by a bridge 
of limited development. The intervening valley is bounded exter- 
nally and internally by a cingulum, which is more prominent on the 
lingual face of the crown. 
The two posterior external tubercles are more massive than 
those placed internally and are always united bv a bridge, reaching 
almost to their summits in an unworn tooth and forming a strong 
external lobe. 
The antero-internal cusp is also well developed, being in every 
case larger than the hind one, not “smaller” as stated by Owen; 
it is joined to the median external tubercle by a slender svgmoidal 
ridge which is much less prominent and less massive than that form- 
ing the external lobe. With wear this group of connected cusps 
develops into an “L” shaped mass, of which the “twisted loop of 
exposed dentine” of Scott f is an extreme form. 
The smaller posterior lingual tubercle is variable in size; it may 
be reduced to a slight swelling on the cingulum enclosing the postero- 
internal portion of the crown, as described in 19121, or it may be 
developed into a mass attaining about half the altitude of its fel- 
lows. It is connected with the anterior lingual cusp by a bridge, 
usually almost obsolete, but on one specimen a strong internal lobe 
sloping backwards is formed by the exceptional development of the 
bridge. 
The cusp is also united to the posterior labial tubercle by a 
weak sinuous connection which varies in extent, being quite distinct 
on the inner tubercle and on the floor of the valley but splitting up 
into a number of faint radiating folds on the inner aspect of the 
posterior external cusp. 
Only in one instance, that exhibiting the maximum development 
of the posterior lingual tubercle and the longitudinal bridge may the 
tooth be considered to resemble the typical example described by 
Professor Owen, as quoted above. The presence of this tooth in the 
collection is taken to indicate that the upper permanent premolar 
is a variable tooth and that the animals in the South-West had not 
succeeded in establishing a distinct species or geographical race be- 
fore they became extinct. 
t A monograph of Nototherium Tastnanicum, Geol. Stirv. record Xo. 4, Hobart, 
Tasmania, 1915, p. 12, and figure. 
X Glauert. Records W.A. Mus., Vol. T., pi. 2, 1912, p. 41. PI. vi.. fig. 10. 
