GENERAL AND INTRODUCTORY. 5 
Haplochiton, A. Seali, 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 essentiaily 
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 Galazias 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 Galazias 
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. 
