IIORX KXPKDITION — .SUMMAUY. 153 



west, and that furtlicr the latter counectiuii has been more niarked than the 

 former, and so has exerted a stronger inlliience. Tiiis miglit Ije Ijrouglit aliout Ijy 

 tile western connection persisting for a somewhat longer time than that on the 

 north and east ; possibly the western connection was established before the eastern, 

 and existed also during the time of the latter. 



Mr. Hedley who, in the Appendix to the Mollusca Report, has dealt with the 

 anatomical features vi a certain nundjei-, lias Icimlly allowed me to reproduce from 

 his correspondence witli nic on the subject the following interesting and suggestive 

 extracts. Mr. Hedley says: "The Rlollusca point clearly t<j an original population 

 derived from Western Australia., composed of Xantliomelon,* Liparus, Pufia, 

 Succinea. Then an immigration primarily from the noithern territory, but 

 remotely from Queensland, is shown by Thersites, Microphyura, 8tenogyra., 

 Bithinia, Melania and Corbicula. This migration from Queensland probably 

 occurred when the Queensland fauna was far poorer than it is now, and as Micro- 

 phyura and Thersites travelled from Queensland, the west sent in e.xchange the 

 few Xantliomelon which have reached the Pacific coast, and which are still 

 conlined to the north. After this, communication with Queensland ceased, so that 

 the rich fauna which lately poured across Torres Straits from New Guinea failed 

 to reach even in one instance to Port Darwin. 



"Another striking lesson to be learnt from an analysis of the fauna is the 

 impenetrable barrier which shut out Tasmanian types. Not a single member of 

 that numerous, active, most enduring group the Ilhytidid;u has reached this region. 

 Originating in Antai-ctia, one colony occupied New Zealand and spread thence 

 through New Caledonia to the Solomons. Another established itself in Tasmania 

 and marched in force to Cape York and even crossed to Mount Owen Stanley in 

 New Guinea. Yet the enormous lapse of time and change of land and water 

 retpiisite for these wanderings was not sufficient to allow Rhytididie to pass into 

 the Larapintinc Region." 



Amongst the land mollusca a very clear distinction occurs between the Lower 

 and the Higher Steppes ; out of twenty-live found in the latter only three extend 

 southwards into the former ; these are (1) Tliersites pcriujlala a widely distril)uted 

 species ranging over the interior from the Burt Plain in the north to the Flinders 

 Range in the south, and westwards to the Fraser Range and Yilgarn in Western 

 Australia, nnd (2) Pupa contraria which Just passes into the northern part of the 



* It will be suuri from tlic Apiiciulix to tlie MoIIuscm Ui_iHJi-t tli.it thu yciicrif iiaiiic of Xarithoiiu-lon is applifil 

 by Mr. Ilfilloy on anatomical grounds to certain species classilied by I'rofessor Tate, respectively, in the jjenera 

 Angasella, (Jhloritis anil Thersites. 



