RECORDS OF W.A. MUSEUM. 
[45 
implanted by two roots, one behind the other, the posterior one 
being the larger and grooved anteriorly, as if preparatory to further 
transverse subdivision.” De Vis defines the upper premolar of 
Zygomaturus in these words': “ Its posterior two-thirds are occupied 
by a longitudinal ridge on the outer side, and two tubercles on the 
inner, the outer ridge and anterior tubercle being joined by a low 
link over which passes the longitudinal sulcus dividing the ridge 
from the tubercles. The anterior third supports a single large 
tubercle or rudimentary lobe.” 
The Mammoth Cave tooth is thus seen to resemble this 
premolar very closely, differing only in the state of development of 
the posterior tubercle of the hind lobe ; in the Zygomatuvus of De 
Vis it is prominently shown, but in the tooth from the Mammoth 
Cave it is only rudimentary. 
Mr. Lydekker states^ that the premolars of Nototherium are 
very variable, and therefore includes under one specific name 
Owen’s various forms of Nototherium as well as the fossils known as 
Zygomaturus trilobus by some authorities. This tooth is therefore 
classed at the upper premolar of Nototherium, and to show its close 
affinity to the Zygomaturus premolar the name Zygomaturus is entered 
as a synonym. 
There seems no doubt that the molar and the premolar from 
the Mammoth Cave have both belonged to the left upper tooth 
series of the same animal, a species of Nototherium. 
^ Loc. cit., p. 114. 
* Ann. and Mag. Nat. Hist., series 6, Vol. III., p. 149, et seq., 1889. 
