292 GEOGRAPHICAL AND GEOLOGICAL DISTRIBUTION. 



ber of species here represented is too limited to permit of much 

 importance being attached to a negative region of this kind. 

 Galaxias attenuatus, a species of southern ' ' trout, " and one of the 

 three species of lamprey are found in New Zealand and the Tas- 

 manian and Fuegian tracts. No fresh-water fishes are thus far 

 known to inhabit any of the islands situated south of the fifty-fifth 

 parallel of south latitude. 



The paucity of the fish-fauna of the tropical Pacific region is 

 very remarkable, and only receives a partial explanation through 

 the circumstance that the greater part of the tract belonging to it, 

 the Australian, is deficient in water-courses. The island of Celebes, 

 for example, which, as has been well urged by Gunther, would 

 seem to offer favourable conditions for the development of a fresh- 

 water fauna, has thus far offered barely more than a half-dozen 

 species, all of them common Indian forms; nor has New Guinea 

 shown itself to be much more prolific. Long-continued isolation 

 has apparently prevented much of the tract from receiving the 

 necessary supply from the fresh waters of continental areas, al- 

 though the identity of existing forms with such as are found else- 

 where would seem to indicate a recent migration and peopling of 

 the waters. The smaller islands of the Pacific are inhabited prin- 

 cipally by such forms, as eels, atherines, gobies, mullets, which 

 can readily exchange fresh water for salt water, and to which, con- 

 sequently, the oceanic basin constitutes no insuperable barrier to a 

 free migration. A species of Arius, a siluroid, inhabits the Sand- 

 wich Islands. 



The marine fishes may be conveniently divided into three cate- 

 gories : shore fishes, or such as habitually frequent the coast-lines, 

 and which rarely descend to a greater depth of water than three 

 hundred fathoms; pelagic fishes, which inhabit the waters of the 

 open sea, the majority of them spawning there also ; and deep-sea 

 fishes, or the fishes of the greater oceanic depths, where the in- 

 fluence of light and surface temperature is but little felt. No 

 sharp line of separation between these several classes is permissible, 

 however, since the habits normally belonging to the members of 

 one class are occasionally assumed by members of the other classes 

 as well, as must necessarily follow from the different conditions 

 governing their distribution. 



