122 DE. B. A. BENSLEY OX THE EVOLUTION 



the Dasyuridge. The hypocone, however, represents at most an outgrowtli from the 

 protocone, the crown-surfaces of the two cusps being practically continuous. Even 

 supposing the upper molars of Notonjctes to have originally possessed a hypocone, we 

 could scarcely expect to find this element differentiated in teeth which have imdergone a 

 consolidation of two cusps, namely the paracone and metacone, which are originally much 

 more distinct from one another than are the protocone and hypocone in the Peramelidse. 

 As shown in PI. 6. tig. 16, there is considerable resemblance between the fourth 

 lower molar of Terameles Bongaincillei and the normal molars of Notonjctes. This 

 resemblance is largely due to the hypsodont condition of ])oth, and since the original 

 condition in the Peramelidie is a brachyodont one, it cannot be strictly regarded as 

 indicative of affinity. A certain resemblance also exists between the fourth upper 

 molars of the Peramelidse with the normal molars of Notoryctes, but this resemblance 

 also extends to the Dasyuridse and Didelphyidae. 



Antemolar Teeth. — Apart from their variability in numbers, the chief feature of these 

 teeth is their lack of differentiation, the incisors, canines, and posterior premolars being 

 all of the same short peg-like character. The median upper incisors are separated at 

 their bases and approximated at their tips, but, like those of the Peramelidse, show 

 otherwise no indications of having been formerly differentiated as in the Dasyuridse, 

 Didelphyidse, and primitive Phalangeridse. The last (morphologically median) premolar 

 is better developed than any of the remaining antemolar teeth, i^robably on account of its 

 association with the better develoj)ed molars. 



PHALANGE RID^. 



The present family has already been referred to as forming with the Peramelidse an 

 intermediate group, with dental characters connecting those of the insectivorous 

 Dasyurinse with those of the herbivorous section. Tlie association of the two families 

 will be seen to depend fundamentally on the recognition of the Peramelidse as Omnivora 

 rather than as Polyprotodontia. The polyprotodout characters may now be considered 

 together with certain progressive omnivorous ones of a lower rank than those seen in the 

 Phalangeridse, as defining the position of the latter family with reference to the 

 Peramelidse as in many respects a derived one. These characters are as follows : — 

 {a) Retention in the Peramelidse of an undifferentiated condition of the median lower 

 incisors, which is replaced in the Phalangeridse by a differentiated condition involving 

 extensive reductions of the antemolar teeth, (b) Retention in the Peramelidse of the 

 piercing character and pyramidal shape of the molar cusps ; replaced in the Phalangeridse 

 by a bunoid or seleuoid modification of these structures. {c) Retention of a full 

 complement of external styles ; in the Phalangeridse these elements are either wholly 

 vestigial (Phascolarctinffi) or absent (Phalangerinse). ((/) Retention of the constructive 

 stages in the formation of either functionally or actually quadrituberculate molars 

 from others of insectivorous type, only indicated in the Phalangeridte, and to a very 

 limited extent, in the development of the hypocone in the upper molars. 



