318 Transactions. 



fresh-water, no marine or relict forms being known to him. Of fresh- 

 water Mollusca he has collected the following : Potamopyrgus corolla Gould, 

 Potamopyrgus corolla salleana Fisher, Isodora *tabulata moesta H. Adams, 

 Latia neritoides Gray, Corneocyclas novae-zelandiae Prime, Diplodon menziesi 

 depauperatus Hutton ; the small fresh-water leech Glossiphonia novae- 

 zealandiae Dendy was discovered in the lake by Mr. Suter, and he has 

 several times seen in it specimens of the fresh-water crayfish Paranephrops. 



It is therefore evident that this little crab is a genuine fresh-water 

 species, and judging from its distribution it must be of very considerable 

 antiquity. Owing to the difficulties of its dispersal across wide tracts of 

 sea by ordinary means, it seems almost certain that the localities at which 

 it is now T found were formerly connected by land, though, of course, the 

 land connections need not have been continuous throughout the whole 

 length of its area of distribution at any one time. Nothing is yet known 

 of the animal's life-history. Presumably it has a free-swimming zoea stage, 

 but even if this could reach the sea from the lakes and rivers in which the 

 adults live it is difficult to imagine how it could cross the seas and ascend 

 other fresh waters so as to account for its present distribution. In one 

 female from Lake Takapuna there are about twenty zoeae lying free under 

 the abdomen of the female. They are of rather a large size for such a 

 small crab ; the abdomen is still folded under the thorax, which is fully 

 I mm. in length, and they appear to have been only recently hatched from 

 the eggs ; the appendages are short and do not look as if they could be. of 

 much use for locomotion, and it is possible that in this species, as in many 

 fresh-water forms, the young are carried about by the female for a longer 

 time than in the case of corresponding marine species. 



Its distribution is an important addition to the evidence showing con- 

 nection between the north of New Zealand and lands lying farther north. 

 A full explanation of the phenomena would involve discussion of the origin 

 of the whole fauna and flora of New Zealand so far as the northern element 

 is concerned, and this would be quite out of place in a paper such as this. 

 It may, however, be desirable briefly to recapitulate what is known with 

 regard to the distribution of other fresh-water Malacostracous Crustacea 

 from New Zealand. 



The New Zealand fresh-water crayfishes belong to the genus Paranephrops, 

 which is confined to New Zealand, its reported occurrence in Fiji being 

 probably due to an error in the locality labels. Three species are usually 

 recognized, of which the one generally known as the northern form, 

 P. planifrons White, is found throughout the whole of the North Island, 

 and also from the north-western and western portions of the South Island 

 — i.e., the north of the great chain of mountains formed by the Southern 

 Alps and their northern continuations. From the discussion of these species 

 of crayfish as given in Mr. Archey's paper in this volume (p. 295) it will be seen 

 that the North Island species, Paranephrops planifrons (White), is composed 

 of two or three varieties, one of which is found only to the north of the 

 parallel of latitude passing through Tauranga, its area of distribution, 

 therefore, corresponding fairly well with the New Zealand area in which the 

 crab Hymenosoma lacustris is found. The fresh-water crayfish of Australia 

 belong to different genera — viz., Astacopsis, Ghaeraps, and Parachaeraps . 

 (See Geoffrev Smith, " The Fresh-water Cravfishes of Australia," P.Z.S., 

 1912, p. 144.') 



The small New Zealand fresh-water prawn, Xiphocaridina curvirostris 

 (Heller), is found in practically all suitable fresh- water streams throughout 



