6 ON THE MANDIBLE OF ZYGOMATUKUS. 



anyone placing the new arrival beside a NototJierium mandible of 

 approximately the same age. 



But are we at liberty to compare the two ? It would 

 appear that before we dare to take that liberty there is a question 

 to be settled. What represents the genus Nototherkim ? Does 

 the genus assert itself to all practical intents and purposes in 

 the mandibles referred to it in 1877, by Owen ; or does it 

 appear in his type specimen only ? It may be well to recall 

 Owen's account of the dental wreck shown by the fossil which 

 nevertheless served him sufficiently well for a type ; he says of it* 

 *' The first tooth," the very important premolar, " is wanting, 

 and the crowns of the rest are broken away," — the only guide 

 to the structure of the teeth left is that " the base of the third 

 remains and gives an indication of a middle transverse valley 

 which most probably separated two transverse eminences." 

 The utter uselessness of this type at the present day, sufficient 

 as it was fifty years ago, when differentiation from Diprotodon 

 was the only thing to be established by it, led me in charity to 

 seek the premolar characteristic of the genus among the examples 

 of Nototherium fossils identified with the type by its propounder, 

 barring of course the cranium in dispute.! This action was 

 declared illegitimate. J 



Suppose the decision were confirmed by general opinion, we 

 must then necessarily fall back on the type ; also we must take 

 the type as we find it described, abiding by the terms imposed 

 upon us ; also we must demand from its describer the same 

 duteous observance of his own conditions as we ourselves have 

 to maintain. The result will be disastrous. 



After arriving at the conclusion that his fossil was from a 

 marsupial of an extinct genus, Owen proceeds to compare it 

 with Diprotodon. " From the jaw of Diprotodon," he says, 

 "the present fossil differs in the much smaller vertical extent of 

 the symphysis, and the convexity of the jaw at its outer and 

 anterior part, and more essentially in the absence of the 

 incisive tusk, and its socket. On these grounds I propose to 



* Brit. Assoc. Report, 1844, page 231. 

 + Proc. Roy. Soc. Queensland, Vol. V., page 3 (1888). 

 J Lydekker— Ann. Mag. Nat. Hist., Series 6, Vol. III. (1889), page 149. 

 Op. cit., page 232. 



