CRUSTACEA OF NEW ZEALAND, 255 



direct descendants from those now living in fresh waters on the surface of the earth. 

 This view has been strongly upheld by some — by Fries, among others — and appeared to 

 receive some support from the fact that specimens of Gammarus fossa rum, kept in 

 darkness during the winter, lost to some extent the pigment of the eyes, thus showing 

 some ajiproach to the blind Niphargi. I shall refer to this again later on. 



Others, again, confining their attention more particularly to the special aflB.nities of one 

 or two genera of the subterranean Crustacea, have pointed out that, in place of being 

 allied to freshwater forms, they more closely resemble marine forms, some of which are 

 inhabitants of deep water. Thus Spence Bate sfcxtes that Nlphargus resembles the 

 marine Eriopis much more than the fresliAvater Gammarus [t, p. 314], and that Craii- 

 (jonyx appears to have its nearest ally in the marine Gammarella [4, p. 326]. This 

 resemblance of the subterranean forms to members of the marine fauna appeared 

 at first to receive some confirmation from the unfortunate name Ccecidotcea [81] 

 given to the blind Isopods from the North- American caves, and from the mistaken 

 ideas as to its affinities ; and, misled by this and by the very imperfect kno\\- 

 ledge of the freshwater Crustacea of New Zealand, I have also stated that the subter- 

 ranean Crustacea of New Zealand appeared to have been derived from a marine source 

 [23, p. <S8]. No doubt the subterranean Crustacea, as well as the freshwater forms, have 

 originally sprung from forms inhabiting the sea, but from the fuller array of facts now 

 before us there can be no doubt that they have not been derived directly from these, 

 but from a freshwater fauna. Nlphargus and Crangonyx may, perhaps, show affinities to 

 marine forms, and there certainly does not appear to be any closely-allied form now 

 inhabiting the surface fresh waters of Europe ; but in North America various species of 

 Crangonyx are found in surface-streams, &c., and the fact that a closely-allied form is 

 found in the fresh waters of Tasmania seems to show that the genus has probably been 

 at one time widely spread in the freshwaters of the globe. CtBckloicea is really a very 

 close ally of tlie freshwater Asellus, species of which are found in the streams of both 

 Europe and North America, with representative subterranean forms in both places. 

 Professor S. I. Smith, in view of the fact that the Crustaceans have several times been 

 referred to as indicating the partially marine origin of the cave-fauna of the Western 

 States of North America, has considered their affinities in detail, and points out thcxt, 

 looking at the Crustaceans alone, there is " no reason for supposing that the fauna of the 

 caves of Kentucky and Indiana has been derived from any other soui-ce than the recent 

 fauna of the surface of the neighbouring region " [104]. The fuller knowledge that we 

 now possess forces us to a somewhat similar conclusion with regard to the subterranean 

 fauna of New Zealand, though here our knowledge is not so complete. The New- 

 Zealand forms at present known are six in number — Gammarus fragilis, Crangonyx 

 eompactus, CaUiop'ms subterraneus, Cruregens fontanus, Phreatoicus typicus, and 

 Phreatoieus assimilis ; and if we consider in turn the freshwater allies of these, we find 

 the following fiwjts : — No freshwater species of Gammarus is known from New Zealand 

 or Australia as yet, but the genus is one very widely distributed and has freslnvater 

 species in other parts of the world; Crangonyx, as has been already pointed out, appears 

 to be exclusively confined to fresh water, species are known either from surface-streams 



