DISTRIBUTION OF SHORE ANIMALS. 



319 



thousands of fathoms, whose inhabitants are usually peculiarly 

 modified for their life in the " utter dark." Generally then 

 we may say that the British Isles stand on a plateau 

 bounded, except at the West, by the fifty-fathom line. 

 The animals which live at the sea-bottom within this area 

 or up to the hundred-fathom line on the West constitute 

 the littoral fauna. This 

 littoral fauna is con- 

 trasted with the pelagic 

 fauna, which includes 

 those animals adapted 

 not for life on the sea- 

 bottom, but for life in 

 the open water, and with 

 the abyssal fauna, which 

 includes the animals 

 adapted for life on the 

 sea - bottom at great 

 depths. Later, we shall 

 have something to say 

 as to the relations of 

 these three faunas ; mean- 

 time we may note that 

 the littoral zoophytes 

 bud off pelagic medu- 

 soids, and that most of 

 the littoral animals 

 (Echinoderms, Crus- 

 tacea, Mollusca, etc.) have 

 pelagic larvae. Further, 

 the fact that the starfish FIG. 

 Henricia sanguinolenta, 

 common between tide- 

 marks, is to be found also at a depth of over 1,000 fathoms, 

 shows that the littoral and abyssal faunas are not sharply 

 marked off from one another. 



We have thus defined the littoral fauna as including, 

 roughly speaking, all the animals which are adapted for 

 life on the sea-bottom in water of under 100 fathoms in 

 depth. In many parts of our area, however, as a bathy- 

 inetrical map will at once show, the greatest available depth 



. "Herring-bone coralline," or Halecium 

 halecinum. After Hincks. A common littoral 

 zoophyte. 



