BY C. W. DE VIS, M.A. 7 



indicate the genus, etc." The species he names inenne, and he 

 then goes on to describe a second species, X mitchelli, from the 

 hinder half of a jaw which he must necessarily have assumed to 

 have been equally devoid of an incisive tusk during life. It 

 follows that no jaw containing such a tooth can belong to 

 Nototherium, consequently that all the fossil jaws, the type of 

 N. mitchelli included, referred to it by Owen himself, or by whom- 

 soever has followed his lead, must be withdrawn from the genus, 

 since they either possess, or can be shown by intercomparison 

 to have, in their perfect condition, possessed incisive tusks. The 

 genus will thus be represented by the unique, and probably 

 abnormal, specimen named N. inenne. Refuge from the catas- 

 trophe will of course be sought in the latitude allowed to authors 

 should experience shew that the generic definitions with which they 

 deal are inexact in detail, or too narrow in scope. A frank 

 straightforward amendment of a genus by its orginator is 

 unobjectionable ; even a silent desertion of the " most essential '• 

 character of a genus may be condoned for the sake of preserving 

 long established names. But then, if an author be permitted to 

 amend and enlarge as he goes on, his amendments and additions 

 become parts of the diagnosis of the genus, and it is clear that 

 an opponent of any one of his determinations cannot be denied 

 the right of appeal to characters so introduced unless it is shewn 

 that such characters were erroneously introduced. To deny the 

 right in the present case is to stand between the horns of a 

 dilemma ; we must either adopt a new name for all these 

 mandibles with incisive tusks, or allow others at their discretion 

 to take their stand upon the generic characters inherent in them. 

 Presuming that this is the alternative which will recommend 

 itself to most minds we will again compare a Zygomaturus fossil 

 with a Nototherium exemplar other than the type. 



The present mandible is from an individual past maturity ; 

 the ridges of the hindmost molars are worn down half way 

 to the base, the foremost has no trace of ridge or valley to be 

 seen in it ; a further proof of age is that the hinder lobe of the last 

 molar has in the forward travel of the whole series advanced to 

 the level of the base of the coronoid process. On the right side 

 of the jaw all the teeth are in place, but m*, mS and the 



