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 type 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 
young 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 entirely 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. 2 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 M. titan. This groove is present in the 
mandibles considered co-specific by Owen, and is invariably so in 
locally preserved examples. 
Finally, the form and extent of the anterior talon of M. 
titan are very different from those of M. mayister at the same 
age ; 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 examples of M. 
titan with his Wellington Valley type must be disallowed. It 
was a judgment, be it observed, delivered ex cathedra without 
reason assigned. 
