BY GEO. M. THOMSON, F.L.S. 47 



and more. It is just questionable whether my specimens 

 are strictly referable to the genus NijjJiargus, occurring, as 

 the latter does, only in the subterranean waters of Europe. 

 The genus is probably of considerable antiquity, for it has 

 undergone a good deal of modification. N. montanus is also 

 probably of very considerable age as a species, for not only 

 does it occur at a much greater elevation than N. mortoni, but 

 it has also undergone greater modification of structure. It 

 would aid us, perhaps, in the elucidation of this problem if all 

 the fauna of the pools on Mt. Wellington were to be examined. 

 The researches conducted by Mr. Chilton and myself on the 

 New Zealand Crustacea have brought to light some interest- 

 ing facts in this connection. For example, of fresh- water 

 Amphipoda and Isopoda there are eight known species in 

 New Zealand, three of which occur in streams, etc., and five 

 are subterranean — of the former, Iclotea lacustris ranges from 

 brackish waters, just above tide-marks, to a height of 1200 ft. 

 The species belongs to a genus having several marine repre- 

 sentatives in the New Zealand, and is apparently identical 

 with a form found in the Straits of Magellan. Our species 

 therefore is apparently in course of development into a truly 

 fresh-water form. One species of Pheriisa (marine) occurs 

 in the shallow coastal waters, another, very different, has 

 only hitherto been found at elevations of 2000 feet, quite 

 100 miles from the sea. One species of Calliopius is marine 

 (littoral), one occurs in fresh-water streams, and a third in 

 the underground waters of the South Island. On the other 

 hand, Gammarus fragilis, Crangonyx compadus, Phreatoicus 

 typicus, and Gruregens fontanus are all species occurring only 

 in subterranean waters, and of which no related marine 

 species have been found. They have very probably been long 

 isolated, especially the two last, and have undergone a very 

 considerable amount of modification. It may ultimately be 

 possible to trace the developmental relations of several of 

 these fresh-water forms from allied marine forms now occurr- 

 ing in the adjacent seas, and this is being gradually done in 

 New Zealand. In the case of Tasmania however, so little is 

 yet known of the Crustacean fauna, that any speculations as 

 to the origin of the fresh- water forms are premature. In 

 light of the finds recorded by me, however, naturalists will 

 wait with some impatience for further researches on the 

 fresh-water fauna of Tasmania. 



The terrestrial Crustacea are of very great interest as bear- 

 ing on the question of geographical distribution. Talitrus 

 sylvaticus is an Amphipod common to Tasmania and the 

 eastern parts of Australia. It is the representative in damp 

 woods of the New Zealand Orchestia sylvicola. How widely 

 these species differ, or whether they are not indeed too 



