260 THE INCISORS OF SCEPARNODON, 



second species whose upper tooth is constantly abraded to an extra- 

 ordinary degree, the lower tooth in both species being unknown. 



The Queensland Museum possesses a perfect adult incisor of 

 large size (PL xxii. fig. 1) ; that this is, without shadow of doubt, 

 an upper tooth is certified by the presence of the premaxillary 

 bone which encases it to a distance of 41 mm. from its outlet, and 

 re-appears distad as a smaller adherent portion from the root end 

 of the socket. In passing it may be noted that the outer edge of 

 the premaxilla, commencing near the outlet, folds over inwards 

 and downwards, also that its inner edge (17 mm. in length) is 

 smooth and entire, showing no sign of sutural union with its 

 fellow, both features foreign to the near kindred of Phascolonus. 

 The working surface of this tooth has the same general length as 

 that in Owen's fig. 5, namely, 13-5 mm. The entire breadth of 

 the tooth being 40 mm., or three-eighths greater than that of its 

 younger type, we may gather that the working surface did not, on 

 the whole, lengthen with age, a fact directly opposed to the 

 assumption that the elongately worn teeth are from the same seat 

 of growth, and at the same time rather discouraging than other- 

 wise any suspicion that they may have belonged to another species. 

 On the concave side of this tooth there is not the slightest trace of 

 a median longitudinal ridge. Assuming for a moment that the 

 subject of fig. 7 is a cast of a lower tooth, its breadth, 35 mm., is 

 fairly proportionate to that from the upper jaw, 40 mm. 



The upper tooth being ascertained and its characters definable, 

 we have to account for those Sceparnodon incisors which are not 

 at all in accordance with it. And here the writer must take 

 leave to confess that, until the last piece of evidence fell into his 

 hands, he, relying on authority, failed to appreciate the differential 

 characters of the teeth and casts under his own observation. His 

 attention to the matter was aroused by the appearance of the 



