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 

 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 



Fig. 386. Archaster mirabilis. ^. (Perrier.) 



