GENERAL AND INTRODUCTORY. 



Haplochiton, H. Seaii, has been chronicled by Mr. R. M. Johnson* as occurring in 

 shoals in the waters of the river Derwent in South Tasmania. It is locally known 

 as the " Derwent Smelt." It is noteworthy in the case of the several Australian 

 fresh-water fish genera Galaxias, Prototroctes, and Haplochiton that, while possessing 

 South American allies, they are not, as in the case of Osteoglossum and Ceratodus, 

 previously referred to, represented also upon the African Continent. Both here 

 and in other instances, where a near relationship can be apparently established 

 between Australian and African organic types, the representative forms are essentially 

 tropical or sub-tropical species. Where, on the other hand, the affinities with 

 South American types alone obtain, the specific forms are limited in their distribu- 

 tion to the extreme south or temperate regions of their respective areas. These 

 circumstances would seem to warrant the anticipation that the intercontinental 

 continuity of Australia with the south extremity of South America persisted for a 

 longer interval, and to a much later period, than that between Australia and a greater 

 or less extent of Africa. The very fact, indeed, of the survival of Galaxias attenuatus 

 in an unaltered form in the several isolated localities above enumerated affords 

 substantial testimony in this direction. According to the generally accepted biological 

 axiom " two identical species are never independently developed in remotely separated 

 localities." This axiom, logically applied to the present distribution of Galaxias 

 attenuatus, involves the unavoidable inference that its existing widely-isolated colonies 

 must have originated from a common centre, between which and its present habitats 

 there must have been a close land connection down to so comparatively recent a 

 date that even the essential diagnostic characters of the fish have remained unaltered. 

 The flightless Struthious birds, comprising the ostrich tribe and its allies, are 

 most commonly cited as affording by their geographical distribution the most 

 substantial evidence in demonstration of a pre-existent common centre of origin in 

 the shape of an extensive Antarctic Continent. In this direction, the Australian 

 region is especially rich. It possesses in conjunction with the neighbouring island of 

 New Guinea two representative genera of the order as typified by the Emu, Dromaius, 

 and one or more species of Cassowaries, Casuarius. While New Zealand is now in 

 possession of but one living generic representative of the order, the well-known 

 " Kiwi " or Apteryx, this now remotely separated island group was formerly the head- 

 quarters of the redoubtable Struthious race, which is exemplified by the giant " Moa " 



* R. M. Johnson, Proc. Zoo. Soc., 1882, p. 128. 



