240 FISHES. 



bution to be one of the oldest Teleosteous types. There 

 must have been a long gap of time before these ancient 

 types were joined by the other Teleostei. All of them 

 migrated through the intervening parts of the ocean from 

 India. Most of the Plotosina, some of the Arii, Dides, and 

 the Atherinichthys, also Nannoperca (allied to Apogon), were 

 among the earliest arrivals, being sufficiently differentiated 

 to be specifically or even generically {Cnidoglanis, Nanno- 

 perca) distinguished ; but some others, like Anahas scandens, 

 Lates calcarifer, Dides warginatus, must have reached the 

 Australian continent quite recently, for they are indistin- 

 guishable from Indian specimens. 



In South-western Australia a mingling of tlie scanty 

 fauna with that of the southern temperate parts takes place. 

 Oligorus macquaricnsis (The Murray Cod), which has a con- 

 gener on the coast of !N"ew Zealand, ascends high up the 

 Murray river, so that we cannot decide whether this Percoid 

 should be located in the Tropical or Temperate part of Aus- 

 tralia. Several Galaxias also extend to the confines of 

 Queensland, and will probably some day be found members 

 of this region. 



In the smaller Pacific islands the Freshwater fishes ex- 

 hibit a remarkable sameness : two or three species of Dules, 

 several Eels, an Atherine, or some Gobies, Mullets, and other 

 fishes which with equal readiness exchange fresh for salt 

 water, and which would at once reach and occupy any streams 

 or freshwater lakes that may be formed on an island. 



The Sandwich Islands are the only group among the 

 smaller islands which are tenanted by a Siluroid, a species 

 of Arius, which is closely allied to Central American species, 

 and, therefore, probably immigrated from Tropical America. 



II. Northern Zone. 

 The boundaries of the Northern Zone coincide in the 



