THE LAND CRAYFISHES OF AUSTRALIA. 113 



material, it is necessary to correct an eiror of interpretation, 

 publisiied in the account which one of us gave of the Freshwater 

 Australian Crayfishes in the ' Proceedings of the Zoological 

 Society ' for March 1912 (p. 144). This account did not pretend to 

 deal with the Land Crayfishes of the genus Evgceus except in a 

 very general manner, but in treating of the geographical distri- 

 bution and relationship of the Australian Oiayfishes as a whole, 

 certain statements were made as to the probable derivation of 

 EngcBtis from the freshwater form Parachcercqjs hicarinatus, 

 which a more detailed study of Engceus has shown to be entirely 

 mistaken. Since the rectification of this error has an important 

 bearing on the geographical distribution of the group, and clears 

 up certain puzzling and unsatisfactory features of the problem, 

 we feel it right to give it some prominence, in order to pi-event 

 the misconception spreading any further. In the memoir- referred 

 to, it is pointed out that there exist in Australia two distinct 

 groups of Freshwater Crayfishes, the genus Astacopsis occupying 

 Victoria, Tasmania, and New South Wales, i. e. the South-eastern 

 portion of Australia,, and the genus Chceraps occupying Western 

 and Northern Australia and New Guinea, but nowhere mingling 

 in its range with Astacopsis. In addition to Chceraps and Asta- 

 copsis with their distinct and limited distributions, there is a 

 single form, the common Parachcpraps hicarinatus, which is closely 

 allied to Climraps in all its anatomical features and is evidently 

 a derivative from Choeraps. This form has spread from the West 

 right into and across the Central Australian deserts, and is now 

 found all over the Australian continent, mingling with Astacopsis 

 in Victoria and New South Wales. It has not, however, pene- 

 trated into Tasmania or New Guinea, which is strong evidence 

 in favour of its being a comparatively modern derivative from 

 Ch(jerap>s. 



As P. hicarinatus is accustomed to live in small water-holes in 

 the desert, it has taken on a wandering and burrowing habit, 

 and is frequently found walking about in fields in search of some 

 moist ditch or water-hole. 



Now, it seemed probable that the genus Enyceus, containing the 

 burrowing land forms, and confined in its distribution to Victoria 

 and Tasmania, had been derived from Parachceraps hicarinatus, 

 through an intensification of the habit of leaving the water and 

 burrowing in damp soil. This idea was further confirmed by the 

 curiously close resemblance which some of the Engceus bear to 

 Parachceraps hicarinatus in external appearance. It was there- 

 fore too confidently stated in the memoir referred to that Engceus 

 was probably a derivative of PcLrachcErap)S, Nevertheless, there 

 was a very puzzling feature pointed out, supposing this derivation 

 to be true, viz., that whereas Engceus is represented in Tasmania 

 by two species, the supposed parent form, Parachceraps hicarinatus, 

 is entirely absent from that island, so that it was necessary to 

 introduce one of two rather improbable hypotheses, either that 

 P. hicarinatihs once existed in Tasmania and is now extinct, or 

 Proc. Zool. Soc— 1913, No. VIII. 8 



