50 THE FAUNA OF THE DEEP SEA 



the ebb and flow of every tide differ from tbe 

 dwellers in the open sea. There is, it is true, at 

 every low tide, a migration of part of the fauna 

 of this sub-zone into the next, but still it is suffi- 

 ciently well defined to be allowed to remain in 

 our category. 



The second sub-zone is not so easy to define. 

 The terms ' laminarian ' and ' coralline ' used by 

 Forbes are only applicable to certain geographical 

 regions and must be abandoned for general use. 



We can only recognise one sub-zone between the 

 littoral sub-zone and the abysmal zone, for notwith- 

 standing the important varieties it exhibits in the 

 nature of the bottom, whether it be rocky, sandy, or 

 weedy, the amount of light, the temperature of the 

 w^ater, and the rapidity of the currents, it is not 

 possible at present to point to any general characters 

 of the fauna of its different parts to justify us in 

 subdividing it. 



The name that may be given to this second sub- 

 zone of the neritic zone is the Katantic — the sub-zone 

 of the slopes. 



The last well-marked zone is the abysmal, ex- 

 tending from the 500 -fathom line to the greatest 

 depths of the ocean, one of enormous superficial area, 



