REPOET ON THE HEXACTINELLIDA, 447 



It may be seen from the above that in the north temperate zone, out of 76 localities 

 which were explored with dredge or trawl, only 11 yielded Hexactinellida. In the 

 tropics, out of 99 dredgings or trawlings 22 were successful in the discovery of Hex- 

 actinellida. In the south temperate zone, out of a total of 1 1 dredgings or trawlings, 2 5 

 localities yielded Hexactinellids. Expressed in percentages the results are as follows : — 



In the nortli temperate zone 14-4 per cent, of the explored localities yielded Hexactinellida. 

 „ tropical „ 22-2 „ „ „ 



„ south temperate ,, 24-7 ,, „ „ ,, 



It is thus evident that the north temperate zone is by far the poorest in localities 

 yielding Hexactinellids, and further that not the tropical, but the south temperate zone 

 furnished both absolutely and relatively the greatest number of Hexactinellida. 



The statistics are somewhat different when we consider not the number of localities, 

 but the number of Hexactinellid species. In this connection we see that 



76 dredged and trawled localities in the north temperate zone yielded 20 species = 26'3 per cent. 

 99 „ „ tropical „ 45 ,, =45'4 ,, 



101 „ „ south temperate ,, 36 ,, =35'6 „ 



The tropics are thus richer in species than even the south temperate zone. 



In regard to the proportion of Hexactinellid localities in the entire northern and 

 southern hemispheres, considered in reference to the total number of dredgings and 

 trawlings, the statistics show that in the northern hemisphere out of 126 dredged and 

 trawled localities 22 yielded Hexactinellids, and in the southern hemisphere out of 150 

 dredged and trawled localities 36 yielded Hexactinellids. The percentage proportion for 

 the northern hemisphere is thus 17'4 per cent., and 24'0 for the southern hemisphere, so 

 that the latter contained many more Hexactinellid localities than the former. 



The total number of species found in the north hemisphere was thirty-four, while 

 sixty-six were obtained in the south. If these numbers be collated with the number of 

 dredged and trawled locahties in each hemisphere, we have out of 126 searches in the 

 north 27 per cent., as against 44 per cent, out of the 150 in the south. Thus the south 

 hemisphere is seen to be about twice as rich in Hexactinellid species as the north. 



Of the 50 dredged and trawled localities in the north tropical zone, 11 yielded 

 Hexactinellida, and the number is the same for the 49 localities in the south. This, 

 therefore, gives for the north tropical zone a percentage proportion of 22 per cent., as 

 against 22 "3 per cent, for the south tropics. The above noted important diflferenee 

 in localities pelding Hexactinellids in the north and south hemispheres does not therefore 

 hold true in regard to the tropics. 



The proportions are different when the abundance of species in the north and south 

 tropics is taken into consideration. 



The number of species found in the north tropical zone amounts to 18, as against 32 



