CHAP. IX.] 



THE DEEP-SEA FAUNA. 



433 



I have already adverted to the danger we run in 

 estimating the relative proportions in which any 

 special groups may enter into the sum of the abyssal 

 fauna, by the proportion in which they are recovered 

 by any single method of capture. Prom their con- 

 siderable size, the length and rigidity of their strag- 

 gling rays, and their habit of clinging to fixed ob- 

 jects, the Echinodermata are not very readily taken 



; FIG. 69. Thecopsammia socialis, POURTALES. Once and a half the natural size. (No. 57 1869.) 



by the dredge, but they fall an easy prey to the 

 'hempen tangles.' It is possible that this circum- 

 stance may to a certain extent exaggerate their 

 apparent abundance at great depths, but w 7 e have 

 direct evidence in the actual numbers which are 

 brought up, that in some places they must be woii- 



F F 



