DEEP-SEA FAUNA. 113 



forms. As might have been expected from our knowledge of cave- 

 faunas, and the habits of those animals, there are a number of blind 

 crustaceans inhabiting the deep, as Nephropses, Polycheles, &c., 

 the last in a manner representing the Jurassic Eryon. Many of the 

 species, on the other hand, are profusely phosphorescent. 



Neither of the three more important orders of mollusks, the 

 Lamellibranchiata, Gasteropoda, or Cephalopoda, enter very largely 

 as components of the deep-sea fauna, although of the first two scat- 

 tered individuals are not exactly uncommon at nearly the greatest 

 depths. Leda and Area were obtained from a depth of 16,000 

 feet. The Cephalopoda are the least numerous, and not unlikely 

 the majority of the apparently deep-water forms represent in reality 

 only captures from shallow water. Wyville Thomson has called 

 attention to the remarkable fact that only on one occasion did the 

 officers of the " Challenger " take the animal of Spirula, " although 

 the delicate little white coiled shell is one of the commonest objects 

 on the beach throughout the tropics sometimes washed up in a 

 long white line, which can be seen from any distance." 41 The 

 Brachiopoda, while enjoying a very broad geographical distribu- 

 tion, are by no means numerous, either specifically or numerically. 

 Although seemingly on the verge of extinction, it would appear as 

 though the actual specific diminution since the beginning or middle 

 of the Tertiary period has not been very great. Most of the recent 

 species are technically shallow-water forms, by far the greater num- 

 ber being found above the five hundred fathom line. Ten species 

 range to depths of six thousand feet and over, and one, Terebratula 

 Wyvillei, was dredged in twenty-nine hundred fathoms. All depths 

 have furnished specimens of Polyzoa. 



Our knowledge respecting the bathymetrical distribution of the 

 deep-sea fishes, owing to the difficulty of determining whether the 

 specimens hauled by the net have been actually taken in the depths 

 indicated by the sounding-line, or have been simply captured dur- 

 ing the ascent of the net, is not very precise, and barely sufficient 

 to permit of any general conclusions being drawn from it. That 

 fishes abound at very great depths there can be no question ; but 

 whether they are equally distributed in the great zone lying be- 

 tween the surface and bottom waters, may still be considered 

 doubtful. The researches of the "Challenger" would seem to in- 

 dicate that this intermediate area is largely, if not almost wholly, 



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