Mr. C. W. De Vis on Nototlierium and Zygoraaturus. 259 



chamber in the position thej should occupy. In proof of this 

 I forward for inspection a cast of the maxilla examined. 



Surely the very number and violence of these hypotheses 

 should have warned a judicious observer against the validity 

 of an apparent fact, however specious, wliich threatened to 

 compel him into their toils. 



And now what is the fact ? and is it so patent, so specious 

 even, as to leave us no alternative but to accept it at any cost? 



Of the original skull in the Australian Museum, Sydney, 

 two editions of casts have been issued, one immediately after 

 its discovery and before the matrix had been efficiently cleared 

 from the surface, the other at a recent date after skilful deve- 

 lopment of details. The former, as may be supposed, is an 

 unreliable exponent of its original — for example, it obscures 

 by a ridge representing unremoved matrix one of tlie charac- 

 teristic features of the very tooth in dispute. Of this edition 

 is the copy in the British Museum, a copy not rendered more 

 trustworthy by having been " restored." 



Waiving this general objection to Mr. Lydekker's source of 

 information, an objection which, had he been aware of it, 

 might have deterred him from his fatal tilt against a difficulty 

 of his own creation, I will take up his parable on his own 

 ground. The left tooth, he says, is triangular (rudely sub- 

 triangular I should call it) and shorter than the succeeding 

 molar. Now if Mr. Lydekker accepts my determination of 

 the shape of the Nototheriuni f""- ^, he must in fairness accept 

 also my description of its structure or give reasons for rejecting 

 it. Of structure in relation to the tooth in question he wisely 

 says nothing. The crown of the Nototheriuni tooth is a single 

 elevated subtriangular cusp rather deeply emarginated on its 

 posterior side and wearing down to a bitriangular tract of 

 enamel-edged dentine. The cast of the Zi/gomaturus tooth 

 (a very young tooth according to Mr. Lydekker's favourite 

 hypothesis) shows a crown flatly depressed and broken up into 

 several eminences ; near the fore end of the tooth in its present 

 state one of these eminences is formed by a conical flat-topped 

 tubercle (its flatness the result of wear) corresponding to the 

 anterior of the external tubercles of the fellow tooth ; behind 

 it on the outer side is another eminence corresponding to the 

 posterior tubercle of that side in the homologous tooth ; the 

 two tubercles of the inner posterior region are concealed by 

 a ridge-like remnant of matrix, as before intimated; the ante- 

 rior basal tubercle is missing, lost probably by the same 

 accident which removed a large chip from the inner anterior 

 surface below the base. This loss is the main cause of the 



18* 



