316 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [April 8, 



it was one of the feRest and most destructive of predatory beasts." 

 (Phil. Trans. 1859, p. 319.) 



Again, " the size of the laniary canine in Felis being here trans- 

 ferred to the first incisor, its function as killer was similarly pro- 

 vided for by the approximation to the moving power, through the 

 extreme shortness of both upper and lower jaws, especially anterior 

 to the chief molar. In Felis the small incisors are very little in 

 advance of the canine ; this large tooth is almost at the fore part of 

 both upper and lower jaws ; and in Thylacoleo the relative position 

 of the incisor tusk to the enormous temporal fossa is such as to 

 give it the advantage of a harder or closer grip during the action of 

 the powerful temporal muscles." And further, " the chief business 

 of the teeth has been delegated to the tusks and carnassials ; deve- 

 lopment has been concentrated on these at the cost of the rest of the 

 normal or typical dental series. The foremost teeth seized, pierced, 

 lacerated, or kiUed ; the carnassials divided the nutritive fibres of the 

 prey. Thylacoleo exemplifies the simplest and most effective dental 

 machinery for predatory life and carnivorous diet known in the 

 MammaHan class." (Phil. Trans. 1866, pp. 79, 80, 81.) 



In the first place, it may be replied that the great cutting pre- 

 molar of Thylacoleo, as has been already shown, bears no real com- 

 parison with the carnassial tooth of the Carnivora, but with the 

 compressed premolar of the Hyjpsiprymni. It would certainly be to 

 the purpose to prove that those Eat-kangaroos which have the 

 largest development of this tooth show specially bloodthirsty inclina- 

 tions, or have any greater preference for animal food than the rest ; 

 but I am unable to find any evidence to this effect. That their diet 

 may be composed more largely of roots than grass and leaves is very 

 probable ; at all events, it is known that the members of the genus 

 are generally more rhizophagous than the true Kangaroos ; and this 

 fact may perhaps afford some indication of the mode of life of Thy- 

 lacoleo*. The Phalangers of the section Cuscus, to which semi- 

 carnivorous habits have been attributed, differ completely from 

 Thylacoleo in the construction of the molars, and especially in having 

 tolerably weU-developed upper canines, though, as before men- 

 tioned, in some of the characters of the skull (the shortness of the 

 muzzle, and verticahty of the symphysis of the lower jaw, and con- 

 sequently of the incisors) they are not so far removed from it. These 

 latter common characters are shared, however, by the purely phy- 

 tophagous and harmless Koala (Phascolarctos) (p. 313, fig. 4). 



With regard to the second question, the peculiar adaptation of the 

 greatly developed middle incisors to a predatory life, exactly similar 

 views applied to Plagiaulax were thus met by Dr. Palconer : — " Let 

 us now test the opinion in its professed character as a physiological 

 deduction. Throughout the Mammalia, where teeth perform the 

 function of canines ' to pierce, retain, and kill,' they are held well 

 apart through the interposition of a line of incisors, the end being ob- 



* The Rat-kangaroos, hke so many other animals, are almost omnivorous iii 

 confinement ; but this circumstance afibrds little indication of their habits in 

 their natural state. 



