TROPICAL PACIFIC EEGION. 239 



tralian continent, as well as to the insignificant size of the 

 fresh-water courses in the smaller islands. Still this cannot 

 be the only cause : the large island of Celebes, which, by its 

 mountainous portions, as well as by its extensive plains and 

 lowlands, would seem to offer a favourable variety of condi- 

 tions for the development of a freshwater rauna,is, as far as 

 has been ascertained, tenanted by seven Freshwater fishes 

 only, viz. 2 Arius, 2 Plotosus, 1 Anabas, 1 Ophiocephalv^s, 1 

 Monopteriis, all of which are the commonest species of the 

 Indian region. New Guinea has not yet been explored, but, 

 from the faunae nearest to this island, we expect its fresh- 

 water fishes will prove to be equally few in number, and 

 identical with those of Celebes and North Australia ; a sup- 

 position confirmed by the few small collections which have 

 reached Europe. Finding, then, that even those parts of this 

 region, which are favourable to the development of Fresh- 

 water fishes, have not produced any distinct forms, and that 

 the few species which inhabit them, are unchanged, or but 

 slightly modified Indian species, we must conclude that the 

 whole of this area has remained geologically isolated from 

 the other regions of this zone since the commencement of the 

 existence of Teleostei ; and that, with the exception of Cera- 

 todus and Osteoglossum, the immigration of the other species 

 is of very recent date. 



Fossil remains of Ceraiodus have been found in Liassic 

 and Triassic formations of North America, England, Germany, 

 and India; and it is, therefore, a type which was widely 

 spread in the Mesozoic epoch. Although it would be rash 

 to conclude that its occupation of Australia dates equally far 

 back, for it may have reached that continent long afterwards ; 

 yet it is evident that, as it is one of the most ancient of the 

 existing types, so it is certainly the first of the Freshwater 

 fishes which appeared in Australia. Osteoglossum, of which 

 no fossil remains yet have been found, is proved by its distri- 



