REPORT ON THE HEXACTINELLIDA. 



441 



Furthermore, it must be carefully noted that this computation takes into account 

 only the localities, but neither the number of the discovered species nor the abund- 

 ance of specimens. When the number of species are also computed the proportions stand 

 as follows : — 



The total number of Hexactiucllid species found at the 276 Stations explored with 

 dredge or trawl is 89, i.e., 32"4 per cent. At the 125 localities explored in the Atlantic, 

 24 different Hexactinellid species ■were found, i.e., 19"1 per cent, — and of these 

 17 were got from the 79 dredgings or trawlings in the North Atlantic, i.e., 2r5 

 per cent., while in the South Atlantic 46 searches yielded 10 species, i.e., 217 per 

 cent. The 32 dredgings or trawlings in the Indian Ocean yielded 16 different 

 species = 50 per cent. In the Pacific the 119 localities explored by dredge and trawl 

 yielded a total of 56 species, or 47 '1 per cent., and of these 18 species or 38 "3 per 

 cent, were found at the 47 dredgings or trawlings in the northern, and 44 species or 

 61"1 per cent, in the 72 searches in the southern region. 



It is evident that the percentage expression of the abundance of Hexactinellids is 

 quite altered when we consider the number of species as well as the localities of capture, 

 though the relative proportion for the different oceans, or northern and southern regions, 

 is but slightly changed. On this computation the Atlantic, and especially the North 

 Atlantic, is seen to be poorest in Hexactinellids, while the Indian Ocean is richest. Only 

 the southern half of the Pacific appears considerably richer than in the j)rcvious table, in 

 fact even richer than the Indian Ocean. The proportionate richness thus stands as 

 follows : — 



North Atlantic. South Atlantic. North Pacific. Indian Ocean. South Pacific. 



21-5 per cent. 21-7 per cent. 38-3 per cent. 50 per cent. 61'1 per cent. 



The richest localities on the Challenger Expedition were in the Atlantic at the West 

 Indian Island of St. Thomas and at the Bermudas, in the South Indian Ocean in the region 



(ZOOL. CHALL. EXP. — PAUT LUI. — 1887.) 



Ggg56 



