284 FISHES 



Gakocerdo is another large genus of which one species, G. 

 arctiais, is found only in Arctic seas. Thalassorhinus is 

 another pelagic genus. Sphyrna or Zygaena, the hammer- 

 headed sharks, are to a certain extent pelagic, but more fre- 

 quently found living in deep water. Among the Lamnidaj 

 Charcharodon is one of the largest and most dangerous of 

 sharks, attaining a length of forty feet ; it occurs in the 

 tropics ; Lanina cornubt'ca, on the other hand, does not exceed 

 ten feet and lives in the north temperate zone of the Atlantic 

 and Pacific. The huge basking sharks, Cetorhinus or Selache 

 in the Atlantic, and RJiinodon in the Pacific, are slow-swim- 

 ming, harmless beasts, feeding by filtration by means of their 

 gill-rakers ; the latter is the largest shark known, reaching a 

 length of fifty feet. Laemargus borealis is also a large shark, 

 but does not seem to be dangerous ; it lives in the Arctic 

 Atlantic, occasionally wandering southwards. Of the Sub-Order 

 Percesoces the Scombresocidas contribute to the pelagic fauna 

 the well-known flying fishes (Exoccetus), of which there are 

 numerous species in the tropical Atlantic, Indian Ocean and 

 Pacific, and some of the half-beaks allied to HemirJiamplius 

 are found in mid-ocean. Many Stromateidse of the same 

 Sub-Order are pelagic, such as Nomeus, the Portuguese man-o'- 

 war fish, so called from its association with the jelly-fish called 

 Portuguese man-o'-war, Seriolella brama, known as the warehou 

 in New Zealand, common in the South Pacific, Centrolophus, 

 the black fish, and Lirus perciformis, the rudder-fish, in the 

 Atlantic which follow floating wreckage or driftwood and Psenes, 

 of which there are several species found in tropical ocean 

 currents, allied to Nomeus. The Sternoptychidce, Stemoptyx, 

 Argyropelecus, and Polyipnus, provided with numerous luminous 

 organs, are most probably pelagic fishes living at some depth 

 in the daytime and coming to the surface at night. Many 

 Scopelidse, such as the species of Scopelus or Myctoplium itself, 

 have similar habits and also possess luminous organs. Of the 

 spiny-finned fishes (Acanthopterygians) the most character- 

 istic are the dolphin-fishes Coryphcena, and the sword-fishes, 

 Xiphiidae and Histiophoridag ; these are active and powerful 

 swimmers which prey upon other fishes, the dolphins being 

 the natural enemies of the flying-fishes. Many species of the 

 Scombridae or mackerels are pelagic, and in fact it may be 



