188 HORN EXPEDITION — SUMMARY. 



fauna ut' .soutliL'1'11 oriyin. New Zealand was to tlic north connected directly of 

 indirectly with Nortli-east Australia and so passed on to these Acanthodrilus and 

 Microjihyui-a, gaining in return certain animals a,nd plants iiom the Australian 

 legion. It must for example have acquired its Peripatus in some such way. Ity 

 this Antarctic land after New Zealand had lust its connection with it a primitive 

 polyprotodont fauna passed across to Australia, entering the latter in the south- 

 east and th(>nce s})reading gradually over the continent and giving rise therein 

 to the various existing types, whilst in America the same primitive group gave 

 rise to the Didelpliyid;e.* Across this land there also spread the Cystignathous 

 frogs, fishes such as Galaxias, Aphritis and Haplochiton and amongst molluscs, 

 (iundlachia. 



The only way in which it s(;ems possilile to account at once for the presence 

 of forms such as Prothylacinus in the Patagonian Tertiary beds and the absence of 

 any of the Didelphyida^, in Australia is to suppose that on the South American 

 side tlie connection between the Antarctic land and what is now Patagonia was 

 lost at a time comparatively soon after the early polyprotodonts had passed across 

 ami tUu-ing which the Didelphyid;e were being developed perhaps in the more 

 northern part of South America. The Antarctic land must however have been in 

 connection with the Australian continent, perliaps it was in the former itself that 

 such forms as Thylacinus were developed ; at all events the distribution of this in 

 Australia points to its having entered by the .south-east at a comparatively late 

 period. It was confintHl in its distriljution to the eastern and especially the south- 

 east ami did not spread up to the far north or across to the west. 



If, subseipiently, the Antarctic land Ijecame reunited with South America, 

 then this would account for the hnding in the Patag(jnian beds of such foi'ins as 

 Prothylacinusf allied to Australian marsupials, though they apparently became 

 extinct and did not spread fai' ncirthwards. ]5efore any of the typical Anuuican 

 types could pass across the Antarctic land and reach Australia the latter had lost 

 its coiniection with the formei' and thus there would exist the Dasyuridte in 

 Australia and tlie Didelphyidie in South America, and in the latter also certain 

 forms closely allied to Australian types of Marsupials. 



Probably the Patagoinan Cieiiolestes and its extinct allies stand in regard to 

 tludr ilentition, in much the same relationship to the Polyprotodonts as Mr. 



* On tliis svi|ipositioM the Diclulpliid type may be regarded as orijjinatiiij; in .Vincriea and spreading thence 

 across to Euroiic. 



t It is perliaps wortliy of note tliat the relatively restricted distribution of Thylacinus and its extinction on the 

 mainland and iireservation only in Tasmania is curiously paralleled by the extinction of its ally in Patagonia, and 

 its rcsti'iction also to the soutii of tlic continent. 



