BY C. W. DE VIS. 121 



for safe determination that these or some one of them should have 

 the corresponding tooth at least in fair accordance with that of 

 the type tooth as to shape and proportions. According to the 

 "improved figure" of the t3^pe tooth (I.e.) its diameters are 14-5 

 and 11; in adult life its length would be still less in proportion 

 to its breadth. But in the adult mandibles identified with it by 

 their describer the diameters of this tooth are respectively 14 and 

 9-5, 15 and 9, 15-7 and 10, yielding as a mean ratio 14*9 and 

 9-5; whereas, to maintain the typical proportions of even the 

 3^oung tooth, the respective widths should be 10-6, 11-4 and 12-6, 

 or in the mean 11.5. This difference in proportions is quite 

 obvious to the eye, and so far exceeds the latitude in this respect 

 taken by modern kangaroos as to be entirel}- prohibitory of the 

 accepted identification. In no one of scores of specimens whose 

 specific co-identity has been ascertained by tracing them through 

 every phase of dentition, and whose identity with the supposed 

 co-types of M. titan is beyond question, does the tooth show any 

 tendency to exchange its normal elongate form for the compara- 

 tively square shape notable in M. titan. The mean ratio of 

 length to breadth deduced from ten adult examples taken at 

 random is 14-5 : 9, and if we take mandibles equal in age with 

 the M. titan type the difference is of course still more evident; in 

 the young m.- the diameters are 14*8 and 8-8. A further proof 

 of non-identity is the absence of a vertical groove from the hinder 

 surface of the tooth in 31. titan. This groove is present in the 

 mandibles considered co-specific by Owen, and is invariably so in 

 locally preserved examples. 



Finall}^, the form and extent of the anterior talon of J/. 

 titan are ver}'^ different from those of M. 7iiagister at the same 

 ase ; that of M. titan is a semioval with a short minor 

 diameter; that of M. magister is much longer, has straight con- 

 verging sides and a short straight anterior edge. On these 

 grounds Owen's identification of his Queensland examj^les of M. 

 titan with his Wellington Valley type must be disallowed. It 

 was a judgment, be it observed, delivered ex cathedra without 

 reason assigned. y^' 



:a^^'-<X 



