OF THE AUSTEALIAN MAESUPIALIA. HI 



PeRAMELINtE. 



Of sixteen species composing the whole family of the Peramelidse twelve belong; 

 to the genus Perameles of the present division. The latter, therefore, presents nearly 

 all of the dental modifications of evolutionary interest foimd in the family. It 

 also represents the parent form from which the less iaclusive genera Choeropus and 

 Thylacomys have been derived. 



Although the modifications of the molars are comparatively vmiform in this series, 

 the specific variability of the antemolar teeth is so great that a general synopsis of the 

 dental sequence is scarcely permissible. 



Sequence of Molar Fatterns. — The order of specialization is as follows : — Perameles 

 l)oreyana and P. Baffrayana, P. Bougainvillei, P. uastita and P. Gunni, P. CockerelJi, 

 P. moresbijensis, P. macrura and P. obesida. Chceroirm castcmotis is in some respects 

 as specialized as the extreme form P. obesula, but appears to be a derivative of 

 P. Boitgainvillei or a closely allied form. 



As indicated iu the above plan, the most jwimitive modifications relate to P. Doreyuna 

 and P. Paffrayana. This remark, however, applies only to the species studied. The 

 collection contains no examples of the presumably primitive forms P. Broadbentl and 

 P. longicmidata {cf. Thomas, 1888, pp. 240-242). 



The following description of P. Loreyana will apply almost equally Avell to P. Raffrayaua. 

 The third vipper molar of P. Boreyana (PL 5. fig. 8) is of an insectivorous type approxi- 

 mating closely to that found in the Dasyurinse {cf. fig. 2, Smintliopsis leucopm). Tlio 

 only important points of departure are seen in the arrangement of the external styles, 

 and in the addition of a new cusp, the hypocone (%.). As regards the arrangement of 

 the external styles, the Dasyurinse have already been described as presenting a specialized 

 condition, style c being greatly developed, while two anterior styles have been fused 

 together to form a single element ub. In P. Loreyana, as, in fact, in all of the Pcranie- 

 linse, style c is only moderately developed *, while the anterior styles a and b are mucli 

 more completely separate. In both of these characters the Peraraelinic approximate 

 much more closely to the Didelphyidic [cf. PL 5. figs. 1 & 26, Peratherium, Metachinm 

 opossum) than do the Dasyurinte. 



The appearance of the new cusp, the hypocone, is of great significance, since it manks 

 the first stage in the transformation of a picu'cing, cutting, and criisliing tooth into a 

 grinding one, or, in other words, the passage from an insectivorous to an omnivoi-ous 

 condition. 



The remaining upper molars of P. Boreyana differ from the third in exactly the same 

 way as in the Dasyurinte. The first and second are more laterally compressed, and the 

 fourth is reduced througli the loss of the metacone. 



The lower molars of P. Doreyana (PL 6. W^. 12) also approximate closely to tliosc of 



• In the ronitnelinae, and also in the Didclphyul;e, as in thj D;isyurin;v!, stjie c is bettor developed in llio tlist 

 and second molars than in the third, .\llowance should be made for this fact when cnrai)arinf; the figure here 

 given of the third molar of P. Doreijana with those of the second molars of other forms. 



