26 
REVISION OF THE GENUS EUASTACUS 
streams south of this part of the watershed flowing into Port 
Philip and the Kooweerup Swamp. 
This apparently anomalous distribution of elongatus and 
yarraensis supports the views of Professor J. W. Gregory 
and of some other physiographers. 
According to Gregory (37) the Cobaw and Strathbogie 
Ranges formed the original watershed between the Goulburn 
and the Yarra River systems, and owing to river capture the 
watershed has moved southward to its present position. 
King Parrot Creek, the Plenty River and the Lower Yarra 
probably formed one river, the upper part of which (King 
Parrot Creek) has been captured by the Goulburn. Also the 
Yea River and Steel’s Creek formed one stream which 
crossed the basin of the Upper Yarra, where it was joined by 
a tributary formed by the Acheron and the Watts; the united 
streams then passed through the Beenak Gap into Kooweerup 
Swamp and thence to Western Port. The Acheron and the 
Yea have been captured by the Goulburn. 
A glance at the sketch map (flg. 1) shows that this interpre- 
tation of the development of the present river system offers a 
reasonable explanation of the apparently anomalous distri- 
bution of yarraensis. 
Returning to the distribution of elongatus, it has been 
observed that it inhabits the headwaters of the Goulburn 
River and certain tributaries. Up to the time of writing, 
no specimen of the genus has been received from the section 
of the Goulburn River between Alexandra and Seymour, 
although numerous attempts have been made to obtain speci- 
mens. Whether the species will be found to inhabit the entire 
length of the Goulburn or whether it inhabits only the upper 
reaches of the river, remains to be seen. 
With the distribution of elongatus as it stands at present, 
we find that the species follows out the old river system 
indicated by Fenner (36). Fenner considered that the 
Goulburn River originally flowed north to the Murray by 
way of the Barjarg Gap, and that the Broken River originally 
flowed south-west through the Black Swamp and on to the 
Goulburn. It is interesting to see that elongatus is found all 
along the Broken River, in the Goulburn from its junction 
with the Broken to the Murray, and in the headwaters of the 
Goulburn and the surrounding rivers. 
The distribution of a fourth species, E. nohilis (Dana), is 
also curious as far as the present river system is concerned. 
South of the Main Divide this species occurs in all rivers 
from the Latrobe River east to New South Wales and in the 
