BY C. W. DE VIS, M.A. 



113 



have remained a matter of mere conjecture had not the founder of 

 the species subsequently recognised it in a young jaw which 

 retained the tooth so much to lw desired, the premolar. This jaw, 

 figured' on PL 40 of the Foss. Mam. of Aus., then became for all 

 practical purposes the type of the genus and species. 



The ITotothcriums were amongst the commonest of the heavier 

 mammals of the period, as witnessed by the abundance of their 

 remains in the post-tertiary drifts. These have afforded to the 

 Queensland collection fourteen premolars of the lower jaw, including 

 one in a young mandible of the same age as the type specimen, and 

 differing from it only in specific characters. The identity of these 

 with the generic type is indubitable. 



Wherever this tooth is present, the recognition of the lower 

 jaw of Nototherium is easy and certain, but as yet the upper jaw 

 has not been identified with the lower on the only evidence which 

 would bo altogether conclusive, association in the matrix. It has 

 not, however, remained undetermined. On the discovery of 

 Zygomaturus trilobus, Macl., it was decided by Sir R. Owen that 

 this was identical with his N. mitchelli, and under that name he 

 figured it. At a later period the same author also assigned to 

 Nototherium the maxillae referred by Professor Huxley to Dipro- 

 todon. That the later determinations are not tenable has already 

 been pointed out. That Zygomaturus should also be distinguished 

 from Nototherium the same writer now finds himself compelled to 

 suggest on the following grounds : — 



The fortunate discovery of the complete skull of the notothe- 

 roid, for which the name Owenia grata has been proposed, discloses 

 the form of both premolars in that genus, and defines within 

 narrow limits the difference between the two teeth in cognate 

 genera. Both are in general terms simple, unilobate, teeth ; the 

 upper one, sub-triangular in section, has its sub-central conical cusp 

 longitudinally constricted towards the apex : the constriction being 

 still seen in the half- worn tooth in a contraction of the dentinal 

 band as it traverses obliquely the longitudinal axis of the tooth. 

 The lower premolar in this genus is structurally the same as in 

 Nototherium as identified by Owen, therefore the upper one of 



