CEUSTACEA OF NEW ZEALAND. 257 



present Crayfish of Europe belong to a different genus, Astucus, Professor Faxon looks 

 upon the existence of a Cambarus in the Carniolan eaves (if the species really belongs to 

 that genus) as evidence of the former existence of the genus Cambarus in the rivers of 

 Europe [37, p. 42]. In connection witli the latter point it is as well to mention that 

 Packard has stated that Joseph's species, Cambarus sf/jgius, is based only on a single di'y 

 specimen from one cave and remains of the forceps of another specimen from another 

 cave, and that " it seems premature to draw conclusions from such limited facts " [83, 

 p. 119, footnote]. 



Passing on to the NcAv-Zealand forms we find that although six species are 

 known from the underground waters of the Canterbury Plains, only one, Calliopius 

 ■fluviatills, G. M. Thomson, is found in the surface-waters of the neighbourhood, and 

 that this species, though allied to some extent to Calliopius subterraueus, is dissimilar in 

 several points, and certainly not so close to it as is Thernsa ccerulea*. It would there- 

 fore seem that the subterranean forms are more ancient than the present surface-fauna 

 of the Canterbury Plains ; and this is confirmed by the fact that their nearest allies are 

 found in remote situations. Thus Fherusa ccerulea, the nearest ally of Calliopius sub- 

 terraneus, is known only from one situation on the top of a mountain between 200 and 

 300 miles distant ; no allies of Gammarus fragilis nor of Cruregens fontanus are known 

 from the fresh waters of the southern hemispliere ; Crangonyx compaetus has its nearest 

 allies in Europe and North America; while Phreatoicus, Avhich is proved to be an 

 ancient form by the possession of characters common to several ftimilies, appears to have 

 been preserved only in the subterranean waters of New Zealand and on the top of 

 Mt. Kosciusko in Australia. 



Although it is thus probably true that some species of the subterranean fauna are 

 ancient forms that have long since taken up their abode in the vmderground waters, we 

 should naturally expect to find others, especially in the fauna of caves, that have much 

 more lately adopted a cave life and are the direct descendants of surface-species still in- 

 habiting the neighbourhood. Such specimens we undoubtedly do find, and they appear 

 also to show several stages or transitions from surface-forms accidentally carried into the 

 caves up to true cave-inhabiting forms. Thus in the caves of America among others 

 the surface-forms Cambarus Bartonil [83, p. 40] and Asellns communis [83, p. 33] have 

 been found, the specimens of these being more or less bleached and much jialer in colour 

 than the ordinary surface-forms ; again, the cave Myriopod Pseudotremia cavernarum is, 

 Packard says, only a modified form of the widely diffused Lysiopetalmn lactarium, Say, 

 and various other examples of the same kind are also to be found in Packard's work. 



In the same way Schneider has described a subterranean variety of Gammarus pulex, 

 found in mines at Clausthal, which diff'ers from the normal forms of that genus in its 

 pale colour, the partial degeneration of the eye, and the lengthening of the anterior 

 antennae [96]. Mouiez also has found in the reservoir at Emmerin in the north of France 

 a single specimen of a Gammarus which has been modified in much the same way as the 



* I have already pointed out, p. 234, that CalUophis sahterranem should 'perhaps be transferred to Pherusa, but 

 that for the present I have left it in the genus in which it was originally placed, as the limits of these two and other 

 allied genera appear to me to need fre^li and careful definition. 



