OF THE AUSTKALIAX iMAR.SL'FlALIA. 107 



sovios docs not indicate that F. ohesiila is an original or ancestral form. P. nasuta, 

 althoug-h recognized as a member of the long- footed series, is not far removed in the 

 proportions of the pes from P. obesnla. It is more pi'imitive in foot- structure than its 

 ally P. Giinni, witli wliich it agrees in dentition. Botli forms are more j^i'iniitive than 

 P. Jiouffainvillei in foot-structure, but more specialized in dentition. P. Gmini is 

 undoubtodly a derivative of P. nasuta, and in this relation it is interesting to note the 

 tvpically Tasmanian distribution of the latter and the South-east Australian distribution 

 of the former. 



P. BoiiqainviUei is ])robably the ancestral form of both Thjlaconnjs and Choeropus. 

 The chief derivative features of Thylacomys are the further digitigrade development of 

 the pes and the peculiar elaboration of the molai's, in wliich an incipient hypocone, like 

 that of P. BomjainvUlei, has been obliterated by displacement inwards of the metacone. 

 It is interesting to compare the distribution of the two forms : P. BougainviUei is 

 West, South, and South-east Australian, and T/ii/lacoiiii/s West, South, and Central 

 Australian. 



Ch(eroj)ws is tlie most specialized member of the family in foot-structure, and presents 

 a great advance in tliis resjject on Tlnjlacomys, which comes second. Choeropiis is, 

 however, to be regarded as an independent derivative of P. Bougaincillei, since it does 

 not show the peculiar type of molar found in TlnjlucoyDi/s. It is interesting to note 

 again the distribution, which includes, in this case, West and South Australia, with 

 AVestern Kevv South Wales and Victoria. 



KOTORYCTID^E. 



The different opiuions as to the affinities of Notoryctes have already been mentioned. 

 The available evidence is decidedly in favour of Dollo's * suggestion of a relationship with 

 the syndactylous Peramelidae. In the general plan (p. 192) Notoryctes is placed as a 

 terrestrial derivative of the Properaraelidte (hyp.), the presumed arboreal ancestors of 

 the Peramelidse and Plialangeridae. The main facts determining this position are as 

 follows : — [a) Excluding Notoryctes, the primary lines of the Australian radiation mav 

 be defined as insectivorous-carnivorous and insectivorous-omnivorous in their composition, 

 and may be distinguished by the respective absence and presence of a hypocone in the 

 upper molars. Notoryctes is too far advanced in a special insectivorous reduction of the 

 molars to show definite resemblances with citlun" series, [b) The two main lines may also 

 l)e distiuguislied by the fact that tliey are made up respectively of eleutherodactylous and 

 syndactylous types, Notoryctes showing definite affinities with the latter, {c) Unlike all 

 tlie remaining members of the syndactylous line, with the exception of the Paramelida', 

 Notoryctes has retained the polyprotodont modification of tlie autemolar teeth, indicatiu" 



* " Caractures communes aii.x rcramelkliu et aux Xotoryctidie, polyprotoilontic, piedorainaucc du quatiic'me 

 orteil, reduction du deuxiume et du troisicme, syiidactylie de ceux-ci, entocuiioiforme allonge, caissc tvmj)auiquu 

 volumineuso, rotule osseuse, poche s'ouvruut cm ariicre. Ccs deux families proviendraient-ellt's d'uii ancdie 

 conimuu?" ^^Dollu, 1899.) 



27* 



