464 



THE VOYAGE OF H.M.S. CHALLENGER. 



The Rossellidse exhibit an cntu-ely different distribution. The maximum number of 

 species occurs in the zone from 101 to 500 fathoms, whence it decreases very markedly 

 downwards, while two forms were found at a depth of 95 fathoms. 



In contrast to the above, the Hyalonematidse again exhibit a more uniform distribution 

 over the entire bathymetrical range. At a depth of 95 fathoms, a single member of 

 this group {Semperella schultzei) was found, while in each of the successive zones of 500 

 fathoms three to six species occur, until the number sinks to one in the greatest depths, 

 as the following scale indicates : — 



In regard to the Uncinataria alone, what has been noted in regard to all the 

 Dictyonina is even more conspicuous, the maximum number of species occurs in the 

 bathymetrical zone from 101 to 500 fathoms, whence it decreases rapidly downwards to 

 the smallest figures at the great depths. This is expressed in the following scale : — 



