f^ FRESflWATKR CRAYFISHES OF ACSTRAIJA. 1 ")') 



phy.sioga-at«Hcal characters -of these two couritiies. It seeins 

 probable tliat "when the two countries were in actual continuity 

 they together formed a zoological district with many features in 

 common/ distinct from the surrounding countries of Victoria and 

 New South Wales. 



By the aforegoing lines of ai-gument we are able to establish on 

 a secure basis the general coui'se of evolution and the routes of 

 dispersal of the Parastacine Crayfishes of Austialia. We are 

 able to establish with certainty that the widely distributed Fara- 

 chceraps hicarinatus is a comparatively recent derivation from 

 the Western- Australian Chceraps, and that the land -Crayfishes, 

 Engceus, are a still more modern derivative from Farachceraps. 

 We are left, therefore, with Chceraps and Astacopsls as the two 

 primitive representatives of Australian Crayfishes, which, both 

 by their com]:)lete isolation from one another and by their wide 

 distribution, betray a great antiquity. The question as to which 

 of these two primitive genera is the most primitive and represents 

 to the greatest extent the oi^iginal ancestor of the group is a very 

 obscure question. We may, however, make some suggestions for 

 the solution of this problem. 



Since Craydshes in genei'al are emphatically not tropical forms, 

 and since the Australian Crayfishes are only represented in 

 Northern Australia by a single species, C. qnadricarinahis, it i» 

 certain that this form is only a northern straggler, and that New 

 Guinea: and North Australia are not the centre of distribution of 

 the group. Granted that the centre of distribution is somewhere 

 in the south of the continent, have we any light to guide us in 

 choosing between Cluprcqys or Astacopsls as occupying most nearly 

 the original area of distribution ? The genus Astacopsis, on the 

 whole, now lives under conditions more generally characteristic 

 of Freshwater Crayfishes than Chceraps. It is characteristic of 

 cooler regions and is particularly abundant in mountain sti^eams of 

 gi-eat rapidity and clearness ; while the western Chctraps inhabits 

 rivers, more sluggish and clouded in nature, which rather fitfully 

 irrigate a parched country. It seems that Chceraps is already in 

 the grip of those circumstances attendant on a lack of water 

 which have finally resulted in the production of such specialized 

 forms as Farachceraps and Engceiis. This is no more than a 

 suggestion, but if it is true we are led to the conclusion that the 

 more southern Astacopsis, inhabiting the temperate and well- 

 watered mountainous regions of South and South-eastern Au.stralia, 

 retain to the greatest extent the original characteri.stics and 

 distribution of the ancestral form. If this is so, and if the 

 Bassian Subregion is really the centre of distribution of the 

 Australian Parastacidse, we may perhaps include these animals in 

 the array of alpine plants and animals characteristic of this 

 region, which were probably once distributed across the Antarctic 

 Continent and reached their present distribution in South 

 America, South Australia, and New Zealand by this means. 



