64 HORN KXPEDITION — NARRATIVE. 



It is a roinarkal)lo fact, that tho oaitliwonn found in tlio centre of the 

 continent helonp;s to a small series of animals the ancestors of which may perliaps 

 have I'eaclieil Austialia l)y way of the Antarctic regions. On tlie wliole tl\e 

 evidence is in favour of regarding this eartliworm as a lingering relic of a fauna 

 derived from the north-eastern side of the continent during the period prior to the 

 time at which the interior hegan to assume its present state of desiccation. Side 

 liy side with Acanthodrilus lives a small land-sliell, Microplixura Iieiiiiclaitsa, 

 helonging to a genus which Mr. ITedley lias described as being "of higli antifjuity 

 and of Antarctic oi'igin." This genus also is found in Queensland, New Caledonia 

 and the Loyalty Islands. 



Probably Acanthodrilus entered Australia liy way of a land tract extending 

 perhaps not at one, but at intervals of, time, from the north of Queensland south- 

 wards, towards the Antarctic, across what is now New Zealand, which is the 

 headrjuarters of the genus. At all events there is no trace of the latter in 

 Tasmania, Victoria or New South Wales. In the centre it is very local indeed, 

 pj'obably it exists elsewhere, but we only found it in three sheltei'ed and favoured 

 spots, separated by long distances from one anothei-. These three spots were 

 Illamurta in the James Range, I)ag<^t Creek on the .south side of the George Gill 

 Range and the Finke Gorge in the McDonnell Range. Even in these places it 

 was only found in small colonies each of which occupied not more than a few 

 square yards of ground in extent. 



We may, as said above, regard Microphyxra he/iiic/nitsa amongst the molluscs 

 and AcavtJiodrihis ercmiiis amongst the worms as thc^ descendents of ancestral 

 forms which long ago entered the continent, and under very diflerent climatic 

 conditions from those which now pre\ail, migrated inland from the north-east coast 

 and witli change of climate have l)een left stranded in the interior. 



Certainly there cannot have been for a very long time past any introduction 

 of eaithworms into the interior, and it is scarcely likely that this genus — tiie 

 rarest of all earthworms in Australia — should owe its existence in the centre to a 

 chance introduction, whilst none of the, at present abundaiit and characteristic 

 Australian genera, have been similarly introduced. 



Not far from the camp at Illamurta was the rocky ravine through which flows 

 in flood time the Ilpilla Ci'cek. On tlie rugged sandstone cHfi's l>ounding the 

 ravine, pines and lig trees were growing and under the shelter of the latter various 

 molluscs were found ;dive. We had before seen plenty of dead shtdls in the 

 rejectamenta, of the Finke, left lichind when the floods had dried up, but amongst 



