IOC 



teeth : in one, several pairs of incisors intervene between the canines ; in the other, one 

 pair of incisors of large size are present and no canines. The first condition characterizes 

 the " polyprotodont section," the second the " diprotodont section"*. The existing repre- 

 sentatives of the latter group of Marsiqrialia are confined to the Australasian area ; some 

 of the former group are American. 



In both sections there are modifications of dentition, of digestive organs, and limb- 

 structures, which in an interesting degree run parallel with each other, — the arboreal 

 diprotodont Phalangers and Petaurists, e. g., with the Opossums and Phascogales, and 

 the saltatory Bandicoots and Ckaeropm with the Potoroos and Kangaroos; while the 

 gradatory carnivorous Polyprotodonts have no known existing diprotodont correlatives. 



But my knowledge of mammalian organization does not authorize me to assert that 

 the diprotodont type of Marsiqnalia could not be so modified as to subserve carnivorous 

 habits. I recognize no sufficient ground for the confidence that predatory dentition 

 must be associated with three or more incisors antecedent to the canine, or " by the 

 interposition of a line of incisors" between the two canines of either the upper or 

 lower jaw. 



Dr. Falconer, in reference to the known Marsupial genera, asserts: — "In all the 

 carnivorous genera and species, fossil or recent, of which the dentition has been accu- 

 rately determined, there are three or more incisors, followed by a canine, on each side 

 of the jaw, above and below; and the empirically observed result is consistent with a 

 rational interpretation of the arrangement, in reference to their food and the means of 

 procuring it. On the other hand, in all the existing strictly phytophagous genera, there 

 is only a solitary incisor (being that next the axis) on either side of the lower jaw, and 

 no canine "f. I shall presently inquire how far this alleged generalization applies to 

 known existing species, premising that it can only be affirmed as bearing on the inter- 

 pretation of the fossil remains of Thjlacoleo and Plagiaulax, by demonstrating the inac- 

 curacy of my determinations of the dentition of those extinct genera, and by resting on 

 the foregone assumption that no Marsupial genus can or could be carnivorous unless it 

 had the canine or caniniform tooth preceded by three or more incisors, and that " a soli- 

 tary incisor," however shaped and associated with other teeth, must make a " strictly 

 phytophagous Marsupial." 



My endeavours, and whatever success may have attended them, in the interpretation 

 of animal structures, have depended mainly on careful avoidance of antecedent assump- 

 tions of the extent of secondary modifications with which a dentition primarily fashioned 

 for animal food might be associated. I leave my mind open, for example, to deduce 

 consequences from observing the modifications of size, shape, and direction of the " soli- 

 tary incisor on either side of the lower jaw," and the form, size, and number of the 

 premolars, and more especially of the true molars associated therewith. To think or 

 reason otherwise would be simply to argue in a circle, as thus: — "All carnassial Mar- 

 supial genera have incisors as well as a canine ; ergo, no Marsupial genus with a laniari 

 * O.vess ' Anatomy of Vertebrates,' vol. iii. p. 293. t X. p. 351 ; XI. p. 434. 



