44<2 PLAGIAULAX. 



former, as pointed out in my earlier description, 'the pre- 

 molars are inordinately developed, while the true molars are 

 dwarfed and rudimentary in proportion.' The operation of 

 the well-known law of Anamorphosis or Balancement is visible 

 in both. But examples of it are everywhere seen throughout 

 animated nature, in the same organ, without reference to 

 affinity, as, for instance, among the Mammalia, in the canine 

 of Machairodus and of the Musk Deer. Thylacoleo and Pla- 

 giaulax may be regarded as being as wide apart among the 

 Marsupials as the two former are among Placental Mammals. 

 The solitary trenchant premolar in some of the species of 

 Hypsiprymnus is said to attain a very large development. 

 We have the authority of Professor Owen for the statement, 

 that in two Potooroos of New Guinea its antero-posterior 

 extent nearly equals that of the three succeeding molars. 1 

 If the teeth of Thylacoleo and Plagiaulax had been on the 

 same morphological plan of construction, the agreement in 

 the number of molars would clearly have carried weight ; 

 but, as such does not appear to be the case, the coincidence 

 ought not to overrule the other indications, more especially 

 as the form of the crowns of the molars in the two genera is 

 totally different. In Thylacoleo, the first tubercular tooth 

 has the crown compressed, supporting two cusps on its axis, 

 the anterior lobe being more or less conical, with a smaller 

 lobe behind it, both on the usual carnivorous type of con- 

 struction. The second tubercular is only known through its 

 socket. In both species of Plagiaulax, the two molars present 

 oblong crowns, supporting two opposed lines of marginal 

 eminences, separated by a depression. In my original de- 

 scription, I referred to the fact that in Dromicia and Acrobata 

 the molars are reduced from the ordinary number, four, to 

 three. In Plagiaulax the suppression is carried still further, 

 two only being developed. The agreement in this respect 

 between the latter and Thylacoleo does not impress me with 

 the idea of affinity, although admitting, as I do, that it ought 

 to be duly weighed. 



I have entered in such detail upon the dental characters, 

 because, by the consent of all observers, they are of paramount 

 weight in the solution of a question of this nature. If the 

 type be distinctly indicated by them to be herbivorous or 

 carnivorous, the other characters, however modified they 

 may be, will ultimately be found to be in relation to the 

 teeth. The author of ' Palaeontology,' having formed his 

 opinion on the teeth, then examines the characters of the 

 lower jaw, and finds them in conformity. He adduces the 

 shortness of the horizontal ramus in proportion to its depth 



1 Odontography, vol. i. p. 389. 



