THE LAND CRAYFISHES OF AUSTRALIA. 115 



guide, and the resemblance to ParachcEvaps^ which proved at first 

 deceptive, consists merely in the absence of spines and ridges on 

 the body and the hairiness of the mouth appendages, which are 

 evidently due to convergence following on the similar mode of 

 life. 



As a matter of fact, in a certain number of anatomical features, 

 besides the gills, Engceus agrees rather with Asiacopsis than with 

 the other two genera : thus the penultimate segment of the second 

 maxillipede projects nearly as far forward as the terminal segment, 

 and the vas deferens is situated on a short simple papilla. 



We therefore have no hesitation in claiming that EiigcBus is a 

 derivative of Astacopsis or of a close ancestral form of Astacopsis, 

 and is fundamentally distinct from the western Ckceraps and its 

 widely distributed derivative F. Mcarinatus. 



It may be pointed out that this conclusion is far more intelli- 

 gible, on general grounds, than the original derivation of Engceus 

 from F. hicarinaUis, and it clears up all the pvizzling features in 

 the geographical distribution of these forms. We can now clearly 

 explain why Engceus occurs as two species in Tasmania, although 

 F. hicarinatus is absent, because Astacopsis occurs in Tasmania. 

 It was also rather unaccountable that F. hicarinatus, being a com- 

 paratively recent derivation from Glioeraps^ which had not been 

 able to penetrate into New Guinea or Tasmania, should have been 

 able to give rise to several widely divergent species of Engceus 

 distributed through Victoria and Tasmania. We can, however, 

 easily see that if Engceus is a derivative from the much more 

 ancient Astacopsis, that there has been ample time for its diver- 

 gence into several species, and its distribution in Tasmania and ' 

 Yictoi'ia alongside the parent Astacopsis, though occupying a 

 totally different station, is perfectly intelligible. 



To sum up the relationships of the Austi-alian Crayfishes 

 as a whole. The western and northern genus Chceraps and 

 the south-eastern genus Astcccopsis have been isolated from 

 one another completely since a very ancient date, and at the 

 present time they nowhere intermingle. Chceraps sent a northern 

 straggler into New Guinea and the Aru Islands at a time when 

 these islands were connected with the mainland (C. quadricari- 

 natus)^ and Astacopsis has a typical representative in Tasmania,, 

 so that this genus in very much its present condition must have 

 been present in Southern Australia at any rate when Tasmania 

 was joined to the mainland. During this period, namely, when 

 Tasmania was joined to the mainland, Astacopsis gave rise to the 

 burrowing Land Crayfishes, Engceus, which are now represented 

 by several species in Victoria and by two species in Tasmania. 

 Subsequently to the separation of New Guinea and Tasmania 

 from Avistralia, the western Chceraps gave rise to an ofi'shoot, 

 Farachcercips hicarinatus, ^\\\(ih, forsaking the rivers as a necessaiy 

 habitat, took to its wandering, pond and water-hole frequenting 

 mode of life, and was thus enabled to spi'ead across the desert 

 regions and invade the territory of Astacopsis in the south 



8* 



