254 DE. C. CHILTON OX THE SUBTERRANEAN 



shown that in many points the resemblance is very great, and that most probably 

 Pherusa ceerulea and Calliopius subterraneus are both descended from a species formerly 

 widely spread in New Zealand. 



This is all that is as yet known of the freshwater Amphipoda and Isopoda ; but it must 

 be remembered that our knowledge of the subject is very imperfect, and that caref al 

 search of other streams, especially in the mountainous parts, Avill probably reveal other 

 forms. As an example, I may mention that until lately Idotea lacustris was known 

 only from the Tomahawk Lagoon near Dunedin, a lagoon situated very close to the sea ; 

 I have, however, since collected a variety of the same species in great abundance in the 

 streams, up to a height of about 1000 feet, around Mt. Mihiwaka, between Port Chalmers 

 and Blueskin, as well as in streams some five or six miles distant, and on the other side of 

 the Waitati valley [21, p. 263]. In the same situations I have also taken another 

 Amphipod, at present undescribed ; this, however, appears to belong to the genus 

 Syalella, and throws no light on the origin of any of the subterranean forms. 



No freshwater Amphipoda have been described from Australia, but in January 1892 

 Mr. Thomson collected two species on Mt. Wellington, near Hobart, Tasmania, and 

 examples of both species have since been kindly supplied to me by Mr. Alex. Morton, of 

 the Tasmanian Museum. They are being examined by Mr. Thomson and have not yet 

 been fully worked out. One is a rather large species, and seems to belong to Niphargus 

 in its general structure and in the uropoda, though the terminal uropoda are not very 

 long. The other species, which is smaller, and comes from the top of Mt. Wellington, 

 about 4000 feet high, also seems to approach very closely to Niphargus, though very 

 different from the pi'eceding species in general appearance ; it closely resembles that 

 species in the antennae, the mouth-parts, and the gnathopoda, which are subequal, and 

 have the propodos subquadrate, as in most species of Niphargus; the telson also is deeplj 

 cleft, not double, and bears stout spines on the hinder margin of each lobe, as inNiphargv^ ; 

 the body, however, is not slender, but rather compact, and the third uropods, though 

 consisting of a very small inner branch and a longer two-jointed outer branch, are not 

 elongated, and the second joint of the outer branch is very small, so that in these respects 

 the animal resembles Crangonyx rather than Niphargus. It is, however, very different 

 from Crangonyx compactus in the gnathopoda, the side-plates, the base of the perseopoda 

 and the pleopoda, and of course also in the telson. However, the species presents a 

 nearer approach to both Niphargus and Crangonyx than any form at present found in 

 the surface-streams of Europe, and it is interesting, because it shows the wide distribution 

 of forms similar to those from which Nphargus and Crangonyx must have been derived*. 



The question of the origin of the subterranean Crustacea has from the first given rise 

 to much discussion and to the most diverse opinions. Unfortunately, too, the question 

 has been obscured by some of the conclusions being based on insufficient facts, and by 

 some of the facts themselves being at first incorrectly stated, as, for example, the 

 affinities of CcBcidofcea. 



The explanation that most readily offers itself is that the subterranean Crustacea are 



* This species Mr. Thomson has named Niphargus montanus, sp. nov. ; the one previously mentioned he calls 

 Niphargus Mortoni, sp. nov., though he tells me he does not feel satisfied about placing it in the genus Nijihanjug. 



