P. BECKLESII AND P. MINOR. 



423 



has been asserted by an able airthority, that, with the excep- 

 tion of the edentate ' species of marsupials, or those which 

 are nearly edentate, like the Tarsipes, and also excepting- the 

 Myrmecobius, all Marsupialia possess four true molars.' L But 

 the character is not absolute, for all the Pigmy-Phalangers 

 of the subgenus Dromicia, besides Acrobata, are admitted to 

 have only three true molars. 2 In the Purbeck fossils the 

 premolars are inordinately developed, while the true molars 

 are dwarfed and rudimentary in proportion. Where such 

 characters coexist with an exceedingly abbreviated alveolar 

 border, there is less reason for surprise in seeing two of the 

 molars suppressed. It is now well known, that there is no 

 certain distinctive character, whether of placental or marsu- 

 pial, that can be founded on the number of their teeth. 

 Among the marsupials, Myrmecobius presents a case in which 

 they are in excess ; while the Purbeck Plagialaux would 

 seem to present the opposite condition, where they are below 

 the normal number, from suppression. 



The same reasons are equally strong for referring Plagiaulax 

 to the neighbourhood of the existing genus Hypsiprymnus. 

 The affinity indicated by the premolars and incisor is so 

 manifest and direct, that details upon the differences from 

 other terms of comparison, placental or marsupial, would be 

 superfluous. The large grooved premolar is confined among 

 the Marsupilia to Hypsiprymnus ; that genus, comprising 

 three subgenera, includes about ten species, in all of which 

 the premolar is solitary, the true molars being constantly 

 four. In Plagiaulax there are either three or four grooved 

 premolars, and only two true molars. In Acrobata and some 

 of the Phalangers, the inferior premolars are as many as 

 four, the true molars in these instances being reduced to 

 three, a dentary formula which closely approximates that of 

 Plagiaulax; while in other Phalangers the premolars are 

 single, the true molars attaining the full complement of four. 



In regard to the indications of the true molars, which 

 might, a priori, have been expected to be the most significant, 

 the tri-tubercular antepenultimate and the longitudinally two- 

 edged last tooth are without a known analogue among living 

 forms. They certainly bear no resemblance to any insecti- 

 vorous species, placental or marsupial. The general form of 

 the tubercles of the antepenultimate suggests some resem- 

 blance to the omnivorous pachyderms, but it is not sufficiently 

 pronounced to counterbalance the strong leaning of the pre- 



1 Waterhouse, Nat. Hist, of Mam- 

 malia, vol. i. p. 8. This generalization 

 ■was previously stated by Professor 

 Owen, in his memoir in the Zoological 



Transactions, vol. ii. p. 333, of the 8th 

 Jan. 1839. 



2 Waterhouse, op. tit. pp. 307, 337. 



