CHARACTERISTIC DEEP-SEA TYPES. STARFISHES. 



107 



There exists in Ar chaster mirabilis (Fig. 386) a remark- 

 able sort of pedicellarise, 

 consisting of two ossicles 

 placed face to face like the 

 hooks of a bracket, each 

 carrying a comb of spines 

 falling one towards the 

 other and forming a very 

 complicated organ of pre- 

 hension. 



There seems to be no 

 doubt that the starfish 

 fauna becomes less and less 

 varied as the depth in- 

 creases, the maximum de- 

 velopment in individuals 

 being found at a depth of 

 from 100 to 250 fathoms. 

 The number of species 

 does not seem to diminish 

 so rapidly as the number 

 of individuals, nor in pro- 

 portion to the variation of Fig , 386 _ Archaster mirabms . 

 the nature of the bottom. 

 Thus in depths of less than 100 fathoms it required 2.7 hauls 

 of the dredge to bring up one species, 15 species and 150 speci- 

 mens being collected in 41 hauls. Between 100 and 200 fath- 

 oms, 21 species and 144 specimens being obtained, the coeffi- 

 cient was 3.6. From 200 to 300 fathoms the coefficient was 

 3.15, with 13 species and 66 individuals. From 300 to 400 fath- 

 oms only 12 individuals were dredged, belonging to 9 species, 

 the coefficient being 3.9. Between 400 and 500 fathoms the 

 coefficient was 4.6. Between 500 and 600 fathoms the coeffi- 

 cient had become 13. We made 15 hauls between 800 and 900 

 fathoms, but obtained only 3 species and 3 individuals, although 

 at a depth of 1,900 to 2,000 fathoms, 4 hauls gave us 7 speci- 

 mens of 4 species. 



Of course the method of carrying on dredgings affects the 



(Perrier.) 



