ITS DISPUTED AFFINITY. 441 



Plagiaulax. If, therefore, the function is to be deduced with 

 such facile certainty from the mere form, the premolar of 

 Hypsiprymnus ought also to be carnivorous. But we know 

 that the genus is so strictly herbivorous that the family to 

 which it belongs has been regarded as representing in the 

 Marsupialia the Ruminants of the Placental Mammals. With 

 this fact before us, is it likely that the premolars of Pla- 

 giaulax were applied to cut and divide flesh ? Does the 

 serrated edge indicate a flesh-cutting function? The sin- 

 gular agreement between the two genera in their premolars, 

 down even to the number of grooves, however trivial and 

 unimportant the character may appear to be, has, I confess, 

 weighed greatly with me in forming my opinion. ISTo special 

 function has, as yet, been connected with the peculiarly 

 grooved tooth of the living Kangaroo Eat. The agreement 

 is therefore purely empirical ; but as the character, according 

 to our present knowledge, is confined, among many hundred 

 genera of Mammalia, to certain species of Hypsiprymnus and 

 to Plagiaulax, those who have faith in the constancy of the 

 manifestations of nature will not lightly believe that it was 

 common to these two genera alone without implying affinity ; 

 and when this is coupled with the obviously phytophagous 

 type of the incisors, the conviction will be confirmed. I 

 need hardly add that I regard the carnivorous deduction 

 from the shape to be arbitrary and untenable. 



[William Hunter, a century ago, by a parity of reasoning, 

 arrived at the conclusion that the Mastodon of North America, 

 from the trenchant form of the transverse crown-ridges of 

 its molar teeth, was an extinct, colossal, carnivorous animal, 

 in short, a kind of predaceous flesh-eating Elephant. 1 The 

 error in his case, as in the corresponding* one of Leibnitz, 

 was excusable, comparative anatomy having been then in its 

 infancy. But it is not a little startling to see the same sort of 

 unsound deduction reproduced, in regard of one of the most 

 pigmy of Mammals, half a century after Cuvier, by his lumi- 

 nous demonstrations, had indicated the method by which such 

 signal mistakes might be avoided in future. — Oct. 15, 1862.] 



Professor Owen perceives another indication of resem- 

 blance between Thylacoleo and Plagiaulax in the proportions 

 of the large premolar to the succeeding molars. In both, 

 there are but two molars, and in so far the agreement is 

 clear ; but no further. In Plagiaulax there are as many as 

 four premolars ; while in Thylacoleo the enormous develop- 

 ment of the solitary premolar or carnassial is effected at the 

 expense of the rest of the premolars, which are suppressed, 

 and of the tubercular teeth, which are dwarfed. In the 



1 Phil. Trans. 1767, vol. Iviii. p. 38. 



