148 



GEODIA AGASSIZII. 



arc concerned this want of correlation is most clearly brought out in the graph: 

 no two of the spicule-dimension curves are near to each other and parallel 

 throughout, lots similar in some respects being invariably different in others. 



This want of correlation of the peculiarities and the results obtained by the 

 comparison of thirty-six pairs given above, force us either to consider all these 

 nine lots of sponges as representatives of the same systematic unit, or to estab- 

 lish a distinct group (species, subspecies, variety, or form) for each one. 



Before entering upon the discussion of this question it will be well to ascer- 

 tain whether there is any correlation between the degree of the difference be- 

 tween the pairs and the distance of the localities where they were obtained. 



As stated, these sponges come from five different regions of the Pacific coast. 

 To ascertain what correlation there is between the distances of their localities 

 and the degree of difference between them in regard to the six spicule-dimensions 

 here under discussion, I arranged the thirty-six pairs of specimens from the 

 different localities in five groups : 1, pairs of specimens from localities in the same 

 region; 2, pairs of specimens from localities in adjacent regions; 3, pairs of 

 specimens from localities in regions between which one other region lies; 4, pairs 

 of specimens from localities in regions between which two other regions lie; and 

 5, pairs of specimens from localities in regions between which three other regions 

 lie. Then the ranges and averages of the differences of these groups of pairs were 

 ascertained for each group. 



To the first group (pairs from localities in the same region) the pairs AB, 



AD, BD, EI, and FG belong; the differences of these pairs range from 8.1 to 

 13.3, their average being 10.6. 



To the second group (pairs from localities in adjacent regions) the pairs 



AE, AF, AG, AI, BE, BF, BG, BI, CE, CI, DE, DF, DG, DI, FH, and GH 

 belong; the differences of these pairs range from 6.5 to 16.8, their average being 

 11.7. 



To the third group (pairs from localities in regions with one other region 

 between) the pairs AC, AH, BC, BH, DC, DH, EF, EG, FI, and GI belong; 

 the differences of these pairs range from 6.1 to 22.5, their average being 14.9. 



To the fourth group (pairs from localities in regions with two other regions 

 between) the pairs CF, CG, EH, and HI belong; the differences of these pairs 

 range from 18.4 to 21.1, their average being 19.4. 



The only pair of the fifth group (pairs of localities in regions with three other 

 regions between) is CH; the difference of this pair is 26.8. 



This shows that the variation of the specimens from different localities in 



