178 HORN EXPEDITION — SUMMARY. 



N(ii' ai^ain in tlie case of tlio iMarsupials dd we liml a,ny distinctisc foriiis, such as 

 wo might lia,ve expected to meet witli, aiiKuigst tin; polyprotndonts, witli tlie 

 single exception of Myimecobius, wliicli however extends liglit across from tlie 

 inland borders of Queensland and New South Wales to West Australi:i, and may 

 just as reas(jnal)ly be regarded as ha\ing wandered across from the east to the west 

 as incc versa. 



It has apparently been sometimes taken for granted that the West Australinn 

 fauna, contains, as contra.sted with the I'est of the continent, ancient anil prinnti\(' 

 forms, but this conclusion is not, at all events so fai' as the higher- forms of life :)re 

 concerned, l)orne out by tlie facts. Amongst the m;irsupials, for (example, the 

 oidy genera confined to it arc to be found amongst the diprotodonts .ind not, as 

 miglit have been expected, amongst the polyprotodonts. 



What constituted the fauna of the large western area, during the time wIkmi 

 the Cretaceous sea separated it oil' from the east we have little menus of ascertnining. 

 Amongst the MoUusca it may have l)een the early ancestors of the Xanthomelon 

 gri^up, a fcnv examples of which passed across the centre to the noi-th-oast; amongst 

 the Amphiliia the peculiarly Australian genera are eastern forms oidy comparatively 

 poorly represented in th(^ western fauna and cannot be regarded as having l)een 

 developed in the west; amongst the Lacertilia perhaps representatives fif the family 

 Pygopodidie and of other forms such as Ampliiliolurus may liave existed, but it is 

 dillicult to believe that eitlier Monotremes or Marsupials can have been present. 



Tt is quite true that the propoi-tion of Polypi'otf)dont species present in the 

 west as comjjared with Dipi'otoilont is greater than in the case of Victoi'ia, New 

 South Wales and Queensland, lint this is simply due to the fact that these \\'ere 

 developed on the eastern sidi; of the continent and tlience spr(>ad west and south.* 



This aljsence (if the fact be established) from the western area in times 

 preceding the Upper Cretaceous period of the ancestors of the ]\Ionotreme and 

 Marsupial fauna is of importance in coniicction with the proltable way in which 

 the latter entered Australia, for there has been no direct land connection between 

 tlie north-west and Asia since that pei-iod. If they were not in the western area 

 when it was dismembered then we are reduced to their reaching Australia by one 

 of two routes (1) via an uplifted Torres Straits, and (2) via a south-eastein connec- 

 tion with Antai'ctic lands, and so across to South America. The former loute is 

 practically negatived by the feeble development of the polyprotodont fauna in 



* Ootaileil evidence in regard to this is n'iveii in the author's Presidential Addre.ss to the Bloloi,'v Section, Aiist. 

 Ass, A<Iv. Soi., Uobai-t, ISOO, pp, 118-12n, on " The Fauna and Zoological Kelation.shiiis of Tasmania." 



