12 NOTE ON THE UPPER INCISOR OF PHASCOLONUS. 



from which all the teeth have been lost. This is broken in such 

 a way as to expose the ends of the sockets of the premolar and 

 first true molar. Just above and behind the apex of the molar 

 alveolus there is a deep round cavity which does not form part of 

 tliat alveolus, and, similarly situated in relation to the premolar 

 socket, is a smaller cavity of the same kind more distant from the 

 axis of the skull and on a lower level than the other and separated 

 from it by a sepiment of bone. These t^vo cavities have evidently 

 received ends of the fang of an incisor similar to the ends exposed 

 in the fossil premaxillary. As the shape and size of the alveoli 

 in this specimen prove it to have belonged to the skull of Phas- 

 colonus we have in it a confirmation of the validity of the reference 

 of the incisor to that genus. 



Among a number of large teeth which have at various times 

 been set aside as incapable of recognition is a nearly entire right 

 incisor, smaller than, but in all essential points agreeing with, 

 that of the present fossil, the chief diflferences being that its 

 lateral grooves are narrower, the columns formed by them less 

 unequal in size, and their extreme ends apparently not so far 

 separated from each other, but the last particular is uncertain, as 

 the part is much mutilated. The anterior portion of this tooth 

 tapers slowly from the outlet forwards ; the lateral grooves are 

 continued to the cutting edges ; the enamel investment of the 

 upper surface extends over the inner but not over the outer 

 groove, consequently the iriner edge of the surface of wear is the 

 longer, and it formed with that of the contiguous tooth a sharp 

 longitudinal ridge from which the abraded surface of dentine 

 slopes outward and upward to the outer angle of the enamelled 

 edge. The worn surface of the tooth is undulatory and 37 "5 mm. 

 in length. The whole tooth is 145mm. long; at its thickest part 

 near the centre its diameters are 31*5 and 26*5. It has a moderate 

 curve in its whole length and is more curved on its upper than 

 on its lower surface. 



The discovery of this tooth must set aside all speculation as to 

 the identity of Scejxirnodon with Phascolonus. 



The premaxillary fossil is from Cambooya, the maxillary from 

 Chinchilla, both localities on the Darling Downs. 



