138 A NATURALIST IN TASMANIA ch. 



Zealand, South Africa and South America, nowhere 

 reaching the tropics. One species, G, attenuatus 

 (Fig. 27, p. 106), is actually common to Tasmania 

 and Terra del Fuego. It has been held to be an 

 explanation of the distribution of this fish that it 

 is known to descend into the brackish water of 

 estuaries, but the enormous stretches of deep ocean 

 now separating Tasmania and Terra del Fuego are 

 really as insurmountable a barrier to the distribution 

 of an estuarine fish as of a truly freshwater one. 

 From the greater community existing between the 

 inhabitants of South America and Tasmania than 

 between any other parts of the southern hemi- 

 sphere, it is probable that these two countries were 

 the latest connected with Antarctica, so that we 

 may suppose that G. attenuatus was distributed 

 along the shelf of the Antarctic continent, and 

 preserved a continuity of distribution for a long 

 time after the actual southern land mass had 

 begun to be split up and submerged. The true 

 freshwater Galaxias, on the other hand, being 

 more completely isolated at an earlier date, have 

 become differentiated into several distinct species 

 in the various southern continents and islands. 

 The other freshwater fishes of Tasmania, the 

 Cucumber Herring (Prototroctes) and the Flathead 

 (Aphritis) also have near relatives in New Zealand 

 and South America, but do not touch South Africa, 

 and none of them extend into the tropics or the 

 northern hemisphere, so that they clearly belong 

 to the remnants of the Antarctic fauna. 



