Chilton. — A Fresh-water Crab and its Distribution. 317 



thought. Its area of distribution was afterwards still more extended by 

 its discovery in the River AYaipa, specimens having been sent to me from 

 that locality by Mr. Cheeseman, and recorded by me in Trans. X.Z. Inst., 

 1912, p. 128. 



To this must be added its occurrence in Lord Howe Island, as mentioned 

 at the beginning of this paper. Mr. Oliver has, however, called my atten- 

 tion to the fact that in 1889 Mr. R. Ethei'idge recorded a fresh-water crab 

 in Lord Howe Island. In his account of " The General Zoology of Lord 

 Howe Island " (Australian Museum, Memoir No. 2, p. 34) he says. " By 

 far the most important member of the Decapoda was Mr. Whitelegge's dis- 

 covery of a fresh-water crab, plentifully distributed in the water-carrying 

 gullies of the North Ridge, behind the Old Settlement, at a height of from 

 200 ft. to 300 ft. above high-water mark. It is a species of Hymenicus." 

 This crab is recorded in the list of species on p. 36 as " Hymenicus sp." 

 There can be little doubt that it is the same species as the single specimen 

 obtained by Mr. Oliver — i.e.. Hymenosoma lacustris (Chilton). 



It will thus be seen that this crab, Hymenosoma lacustris, is known 

 from three localities in the north of New Zealand, from Norfolk Island, 

 Lord Howe Island, and from two localities in Victoria. Australia, and that 

 it is therefore a fresh-water species widely distributed in localities now 

 separated by broad tracts of ocean. 



Its true fresh-water character was not at .first recognized owing to 

 ignorance of the nature of Lake Takapuna, in which it was first found. 

 This lake is situated very near to the sea, its eastern edge being not more 

 than 200 ft, from the high-tide mark in Rangitoto Channel, while its western 

 edge is within 400 yards of Waitemata Harbour : the deepest part is stated 

 to be 168 ft., which is about 100 ft. below the bottom of the neighbouring 

 Rangitoto Channel. It was formerly thought that there might possibly be 

 some connection between the lake and the neighbouring sea, and it was 

 doubted whether there was not a substratum of sea-water in the lake at 

 depths below that of the channel. In 1899 Mr. J. A. Pond undertook the 

 investigation of the waters of the lake, and the following facts, together 

 with those already given, are taken from his paper published in 1900.* He 

 took samples of the water from the surface at various distances from the 

 margin, and also one from the pump-well at the pumping-station which 

 supplies the suburb of Devonport. These samples were submitted to 

 analysis, and "yielded chlorine 2-87 gr. per gallon in each instance, while 

 the total solids at 105° C. were 8-68 gr. per gallon from the lake and Devon- 

 port samples, the pump-well 8-96 gr. per gallon." He also obtained samples 

 from different depths— viz., 50 ft., 100 ft,, 157 ft,, 160 ft., and 163 ft. " The 

 results of analysis gave chloiine 2-87 gr. per gallon, equal to chloride of 

 sodium 4-73 gr. in each sample, while the total of solids gave 8-68 gr. per 

 gallon in each instance, the water from the bottom of the lake being de- 

 canted from the precipitated matter. There is, therefore, not the slightest 

 difference in these two factors of the waters at varying depths, and these 

 agree with our analysis of samples taken at various periods."" 



Mr. Pond's results show the Takapuna is a genuine fresh-water lake 

 without any connection with the neighbouring sea. This character is also 

 confirmed by the fauna of the lake, for Mr. H. Suter, to whom I applied 

 for information, informs me that the general fauna of the lake is decidedly 



* Pond, J. A., "On the Percentage of Chlorine in Lake Takapuna," Trans. X.Z. 

 Inst., vol. 32, pp. 241, 242. 



