HORN EXPEDITION—ZOOLOGY. APPENDIX. 
417 
another and from the rest of the continent by tracts now absolutely impassable 
to an earthworm. 
We are bound therefore to regard this species as a survivor of the old 
earthworm fauna, which almost entirely disappeared when, in Post-Pliocene times, 
the climate changed and the country gradually dried up, preventing a migration 
of earthworms, and gradually driving back those which did persist into their 
present isolated and sheltered homes amongst the Mountain Ranges. 
Though it would be rash, on evidence as yet so slender, to speak with 
anything but considerable hesitancy upon the matter, still it is perhaps worth 
while suggesting an interesting point brought out with regard to the early earth¬ 
worm fauna of the continent, supposing, what really seems likely, that the genus 
Acanthodrilus is the only one found in the central area. 
It shows, at all events, the antiquity of the genus (for I feel sure that it is 
not an introduced form), and it tends to show, inasmuch as it has been found in 
three isolated spots far distant from one another and in conjunction with no other 
form, that at an early period the genus Acanthodrilus must have been the 
dominant one in that part of Australia from which the central area derived its 
earthworm fauna. It is of course possible that other genera existed l)ut were 
unable to accommodate themselves to change of environment; even were this 
the case, it would still tend to show the dominancy of the genus Acanthodrilus. 
Now, if we take the distribution of Acanthodrilus, we find that it is repre¬ 
sented by one species in North-west Australia,* two in Queensland (I have a 
third as yet undescribed species from the Mary River district), numerous species 
in New Zealand, where it is now the dominant genus; and species scattered over 
New Caledonia, Falkland Islands, Kerguelen, etc.. South America, and the Cape 
of Good Hope. 
As Mr. Beddard has already indicated, the genus is probably to be regarded 
as a southern or Antarctic one, owing its present distribution to a former more 
genial climate and greater extent of land surface in Antarctic regions. 
So far as Australia is concerned, it seems to show (1) that members of the 
genus entered towards the north, coming up from the south by way of a land 
connection to the east of the present continent, and so not apparently touching 
Tasmania or the south-eastern part of Australia, where the genus is not repre¬ 
sented; and (2) that they formed the more important element of the earth- 
* Fletcher, Proc. Linn. Soc. N.S.W. (iv.), 1893, p. 999. 
