88 FOSSIL MAMMALIA OF THE 



ill the poepbagous and rliizophagous Marsupials. Dr. Falconer states, " So far as can 

 be seen " (in fig. 7) " the depression would seem to be more limited " than in llypsiprym- 

 nus, where the " crotaphyte depression terminates in an excavation common to it and the 

 dentary canal." ^ 



I conclude, therefore, that, in this ' fifth specimen,' as in the type of Plagiaulax 

 Bec/clesii, the ascending plate or ' ramus' is entire, as in Basyurus and Thylaciniis, with 

 a like carnivorous character of coronoid and condyle. 



\ XVII. — Taxonomic deductions. 



In the non-production of an angular process of the mandible downward and backward 

 below a condyle low-placed as in Plagiaulax, in the inflection of the part corresponding 

 to the angular process in placental Carnivora and its continuation with a similarly 

 inflected lower border of the ' ascending ramus,' with a corresponding outwardly pro- 

 duced ridge deepening and bounding below the outer crotaphyte depression, I see, with 

 Dr. Falconer, characters of the mandible of Plagiaulax which " are clearly marsupial." " 



In this ancient extinct marsupial genus the mandibular dentition is : — 



^ r^' ^ 0^' P 4^' °^' 3^' ''* 2^' ^ 14 or 12. 



In this formula the ' premolars' are defined by ' shape.' 



Now, the Marsupialia show two leading modifications of the anterior mandibular teeth: 

 in one, several pairs of incisors intervene between the right and left canines ; in the 

 other, one pair of incisors of large size are present, and no canines. The first condition 

 characterises the ' polyprotodont section,' the second the ' diprotodont section.'^' The 

 existing representatives of the latter group of pouched Mammals are confined to the 

 Australasian area. Some of the former group are American. 



In both sections there are modifications of dentition, 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 ; the 

 saltatory Bandicoots and Choeropods with the Potoroos and Kangaroos : the gradatory 

 carnivorous Polyprotodonts have no known existing Diprotodont correlatives. Plagiau- 

 lax belongs to the diprotodont section of Marsupialia, and the next step is to determine, 

 so far as the mandible and mandibular dentition may support a deduction, to which of 

 the minor groups or families of that section it shows the nearest affinity. 



^ Loc. cit., p. 2/1, and torn, cit., p. 421. 

 ^ Loc. cit., p. 2/1, and torn, cit., p. 421. 

 3 Owen ' Anatomy of Vertebrates,' vol. iii, p. 293. 



