DISTRIBUTION AND LOCATION 283 



forms ; the north coast belongs to the East Indian region and 

 its fishes resemble those of India, while those of the south coast 

 are similar to those of New Zealand. The east coast having 

 the largest and the most advanced population, the fishes are 

 naturally best known on this coast, in the middle part of which 

 tropical and south temperate species mingle together. One of 

 the most celebrated genera of Australian fishes from the bio- 

 logical point of view is Phyllopteryx, the species of which are sea- 

 horses resembling the Hippocampus of Europe, but with many 

 of the dermal bony plates produced into long processes which 

 terminate in long irregular membranous appendages. These 

 frond-like appendages have a close resemblance in the water to 

 the fronds of the sea-weeds among which the fishes live ; all the 

 pipe-fishes and sea-horses exhibit protective resemblance in 

 colour and often in shape, but in none of them is the disguise 

 so wonderfully developed as in Phyllopteryx. 



Pelagic Fishes. — By this term is here meant those fishes 

 which habitually live in mid-ocean near the surface ; there is 

 no sharp separation between these and the littoral fishes, 

 especially those of the latter which like the mackerel have 

 pelagic habits, and true oceanic forms, either accidentally or 

 habitually, may approach the coasts. The most characteristic 

 forms are large sharks and spiny-finned fishes (Acanthoptery- 

 gians) ; some Stomiatidae occur, including the Sternoptychida; 

 in this family ; among the Haplomi, Scopelidai are numerous, 

 and among the Percesoces, Scombresocidae occur. Hippocam- 

 pus, the Sea-horse, is one of the forms which drifts with float- 

 ing weed and the Plectognathi are represented by the sun- 

 fishes. The chief subdivision which can be made of oceanic 

 habitats is between tropical and temperate, and as in other 

 cases the number both of species and individuals is greater 

 within the tropics. Of Elasmobranchs pelagic forms natur- 

 ally belong to the Selachians or sharks, the Batoidei or 

 rays being specially adapted to live on the bottom. The com- 

 monest oceanic sharks are species of Carcliarias, thirty to forty 

 in number, some of them twenty-five feet in length : these are 

 tropical and sub-tropical and dangerous to man ; the blue 

 shark, C. glaucus, is one of the commonest but not one of the 

 largest, not exceeding fifteen feet in length ; smaller specimens 

 are frequent on the south coast of England in summer. 



