88 FOSSIL MAMMALIA OF THE 



in the poephagous and rhizophagous Marsupials. Dr. Falconer states, " So far as can 

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

 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 Flagiaulax 

 Becklesii, the ascending plate or ' ramus' is entire, as in Basyurus and Tliylacinus, 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=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: 

 m 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 

 j^ustralasian 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. 271, and torn, cit., p. 421. 



2 Loc. cit., p. 271, and torn, cit., p. 421. 



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



