40 



ON D1PROTODON MINOR, 11UX, 



ence rising from the base of the fore angle of the tooth upon the foot 

 of the lobe — it is much too small to be termed a lobe. 



The welcome advent of a premolar in connection with its 

 cranium fixes the identity of two similar teeth which had been 

 previously referred, but with hesitation, to D. australis. From one 

 of these, the premolar of a series exactly equal in both dimensions 

 to that of the cranium aforesaid, we learn that the tooth at an 

 earlier stage of abrasion was incomplete accord with the anticipation 

 already expressed — the dentine forms a f| shaped loop, the legs of 

 which are separated by their enamel edg^s — the edges themselves 

 meeting upon the line which is afterwards to appear as the linking 

 tract of dentine. The third example shows us on the otli^r hand 

 the aspect of the tooth at a greater age — the only differences are a 

 broader continuous band of dentine surrounding a smaller and 

 shallower central pit of enamel. The prebasal tubercle in both 

 these is as insignificant as in the one described. 



Allowing for variation in the size and shape of the prebasal 

 tubercle (scarcely a specific character), and for the changes in the 

 aspect of the grinding surface consequent upon the uncovering of 

 deeper-seated structure, the premolar of Diprotodon australis 

 is generically identical with the premolar figured by Professor 

 Huxley as D. minor. To Professor Huxley, therefore, the merit of 

 being the first to recognise the Diprotodon premolar is ceitainly due. 

 But the fossils examined by him comprised a second premolar, which 

 at the time declared itself to be, without doubt, specifically distinct 

 from the other. Viewed from the outer side, the two teeth are indeed 

 strikingly different, the smoothly convex lobes of the one being in 

 marked contrast with the sharply-ridged surfaces of the other. But 

 assume that the definition of the anterior and posterior depressions in 

 the type of D. minor may occasionally disappear, leaving the mesial 

 indent as we see it in the figure and that by a further modi- 

 fication the abrupt edges of the latter may be removed, and its 

 central line deepened, the tooth as it presents itself in D. (australis ?) 

 will be very near the product. Now, such intermediate condition 

 is opportunely exemplified by the premolar of U. australis, as will be 

 seen from the description ; albeit, the fact proves nothing 

 more to -the point than this, that the possibility of such condition 



