93 



NOTE ON THE OCCURRENCE IN TASMANIA OF 

 THE FRESHWATER CRAB, H7MEN0S0MA 

 LACUSTRIS, OHILTON. 



By Chas. Chilton, M.A., D.Sc, C.M.Z.S., 



Professor of Biology, Canterbm-y College, New Zealand. 

 (Communicated by Professor T. Thomson Flynn.) 



(Received 8th July, 1919. Read 11th August, 1919.) 



Professor T. Thomson Flynn, of the University of 

 Tasmania, of Hobart, has been good enough to send me 

 some specimens of a small crab obtained by him in North- 

 West Tasmania, which he thought belonged to the species 

 Hymenosoma lacustris, Chilton, though they appeared to 

 differ from the pxiblished descriptions in the shape of the 

 rostrum a.nd in some other points. The few specimens he 

 collected were found nestling in the crevices of rotting 

 wood in a very small creek in the middle of an open pad- 

 dock near Flowerdale. 



This species was originally described from specimens 

 obtained in Lake Takapuna, near Auckland, New Zea- 

 land, and has since been recorded fi-om other localities in 

 New Zealand, also from Norfolk Island, Lord Howe 

 Island, and from two localities in Victoria, Australia. Its 

 oeourrence in Tasmania is additional evidence of its wide 

 distribution, and its antiquity. I have coanpared thei Tas- 

 manian specimens with those from the other localities, 

 and consider that they should be placed in the same 

 species. The rostrum is more sharply depressed than in 

 the Victorian specimens, more truncat-e at the end, and 

 its lateral margins are more raised, showing prominently 

 in dorsal view. In the Victorian specimens the rostrum 

 is more nearly horizontal, its margins are less prominent, 

 and the end is somewhat narrowly rounded. The Nor- 

 folk Island specimens have the rostrum, on the whole, 

 similar to that of the Victorian, but the end is more 

 broadly rounded ; in the Lake Takapuna specimens the 

 rcstiiim is much depressed, and the margins are sharply 

 raised, but the end narrows to a blunt point, instead of 

 being regularly rounded. 



Other differences between the specimens then known in 

 tlie lateral teeth on the carapace, the hairiness of the cara- 



