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kish or sea water. New Guinea shews clearly the tact that immi- 

 gration from the sea or from brackish water has played and perhaps 

 still plays a predominant part in the populating of its rivers. 



Let us now return to the point at issue : namely, that the marine 

 fish-fauna of New Guinea forms part of the great Indo-Pacific fish- 

 fauna and particularly of that of the Indo-Australian Archipelago. 

 Keeping this in mind one might be inclined to draw the conclusion 

 that there is not much to be learned from the fauna of the rivers 

 of New Guinea concerning the history of this island. Such a con- 

 clusion however would be erroneous, for it is clear that the very fishes 

 which are characteristic of the fresh-water of New Guinea belong: 



J. to genera which outside New Guinea are known only from 

 Australia (Pseudoniugil, Rhombatractus, Melanotaenia, Eumeda) ; 



2. or to genera nearly related to exclusively Australian genera. 

 Lambertia for instance is nearly related to Eumeda; Glossolepis to 

 Rhombatractus and the three new species of Apogon are closely 

 allied to Australian ones. Finally the species of Hemipimelodus 

 from New Guinea form a special group, distinct from those of the 

 neighbouring Indian Archipelago. Everything that gives to the 

 fresh-water fish-fauna of New Guinea a character different from that 

 of the Indian Archipelago is at the same time characteristic of 

 Australia. Twelve of its species belonging to the genera Pseudo- 

 mugil, Rhombatractus, Melanotaenia. Glossolepis, belong to the family 

 or subfamily of the Melanotaenidae, only known from Australia. 

 ] do not hesitate therefore to maintain that the river-fishes of New 

 Guinea belong to two groups: 



1. A fluvio-marine group, which is Indo-Australian or, if one prefers, 

 Indo-Pacific and which may also be met with, for instance, in Ambon 

 or Celebes. To this category belongs also Rhiacichthys (Platyptera) novae- 

 guineae Blgr. discovered by Pratt in mountain rivers of the Owen 

 Stanley Range four thousand feet high. Boulenger speaks of the disco- 

 very of a fish of the genus Rhiacichthys "so admirably adapted to life 

 in mountain torrents" as highly interesting. He tells us that the closely 

 allied Rhiacichthys asper G. V. is known from Bantam, Celebes and 

 Luzon. This is likely to create the impression that Rhiacichthys novae- 

 gnineae does not belong to this category, but is a species whose neai est 

 relative is confined to rivers in regions occupied by the Asiatic fauna. 

 Rhiacichthys asper however, differing but little from Rhiacichthys novae- 

 guineae, was also found by Bleeker in Sumatra and, what is far 

 more interesting, it occurs, according to Günther, also in Wanderer 

 Bay on the island of Guadalcanal' in the Solomon Islands — in 

 ''fresh- water". At all events it is thus found close to the sea. This 



