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[Read before the Philosophical Institute of Canterbury, 4th November, 1908.]
The immediate cause of this paper was the discovery in February, 1908, of a fresh-water gammarid at Rona Bay, Wellington Harbour, which, on examination, proved to be the same as Phreatogammarus propinquus, a species described in 1907 from a single specimen collected by Mr. Crosby Smith on Mount Anglem, Stewart Island. This species was of special interest as the first species of Phreatogammarus to be recorded from the surface waters of New Zealand, and owing to its near relationship to P. fragilis, a species inhabiting the underground waters of the Canterbury Plains. During the last few years, too, several facts referring to the other freshwater Amphipoda have been collected, and it seems, desirable to gather them together here. This group of the Crustacea possesses considerable interest from the point of view of geographical distribution, and for this reason a paper on the subject was commenced and partly written out about fifteen years ago, but was then left unfinished owing to want of knowledge of the fresh-water Amphipoda of Australia and elsewhere. Since then many of the gaps have been filled up, and, though our knowledge is still far from complete, some comparison of the fresh-water Amphipoda of New Zealand with those of other countries is now possible.
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In this paper, however, I shall give only a list of the various species, with references and notes as to their distribution, reserving more general remarks for a future paper. The three subterranean species have been included because it is around them that the chief interest centres, and because two of them are now known to have near representatives in the surface streams. The terrestrial amphipod Parorchestia sylvicola (Dana) has not been included, because it is truly terrestrial, living far from streams, although it is found only under decaying leaves and in other moist situations, and its method of respiration is doubtless practically the same as that of the freshwater species. It is a species very widely distributed in New Zealand and perhaps elsewhere, and there are various uncertainties and difficulties connected with it that require for their solution more time than can be devoted to the question at present. I have, however, included Parorchestia subtenuis (Dana), as it seems to be usually found in fresh-water streams, though able to live in brackish water, and perhaps also on land. There are other brackish-water species, such as Melita inaequistylis (= M. tenuicornis) (Dana), that I have not included, because, although they may be found in water that at the time is almost or quite fresh, they do not appear to have established themselves in the fresh-water streams.
I have arranged the species according to the classification in Stebbing's “Das Tierreich Amphipoda,” and have given only such references as appeared necessary; others will be found in that elaborate and exhaustive work.