254 



PAPERS FROM THE DEPARTMENT OF MARINE BIOLOGY. 



In future it would be well to seek more direct and accurate results by 

 some method like the following: Select from the sample laid out for deter- 

 mination some grain of fairly regular shape to be regarded as a unit of volume; 

 then estimate and record for each grain studied the number of such units 

 it contains. In this way there will be a record of the number of units of 

 volume of each organic group originally present and thus direct comparisons 

 of unit weights will be possible as far as the volumes were correctly estimated. 

 In any case this will be more accurate than merely recording the number of 

 grains of each group. Where part of a grain is taken for crushing and 

 microscopic study, both the number of units of volume it originally contained 

 and the number of units preserved for weighing must be recorded. Probably 

 it will be best to take one of the smaller grains, though not necessarily the 

 smallest, as the unit; or perhaps some more regular unit (as a piece of shot 

 passing the same sieve as the sample) will be found best. 



Chemical Composition. 

 The chemical composition of each size portion was obtained by calcu- 

 lating the percentage of the four principal salts, CaCOs, MgCOs, CaS04, 

 and Ca3P208, contained in each organic group. The assumed composition 

 of the organic groups was derived from figures given in the manuscript of 

 Dr. Clarke and Mr. Wheeler's unpublished paper.^ Those used in the 

 calculations for this paper are tabulated herewith:^ 



Corallinaceae 



Halimeda 



Mean alga 



Madreporaria 



Alcyonaria 



Mollusks 



Tinoporus 



Amphistegina 



Orbitolites 



Poly trema 



Approximate average foraminifera . 



Crustacea: 



(i) Malacostraca and ostracods. , 

 (2) Balanus 



Sea-urchin spines 



Worm-tubes 



CaCO, 



77.00 

 98.50 

 90.00 

 91.00 



MgCO, 



19.00 

 •so 



9-75 

 .70 



15.00 



•25 

 11.00 

 4.80 

 10.60 

 11.25 

 10.50 



12.50 



i-SO 

 9.00 

 8.00 



CaSOi 



1. 00 

 .50 

 •7S 



1. 25 



CaaPjOs 



8.00 



8^7S 



In a few cases of individual species of foraminifera, etc., these figures 

 could be taken directly; but in most cases some sort of compromise, which 

 was not at all a mathematical averaging, had to be made. The reason for 

 not taking an average was mainly that many forms show a tendency to an 

 increased percentage of MgCOs with increase in temperature of the water 

 in which they live; hence forms from environments corresponding more or 

 less to Murray Island had to be favored in deriving the figures. Further- 



'F. W. Clarke and W. C. Wheeler. The inorganic constituents of marine invertebrates and calcareous algae. 

 The combinations of acid and basic radicals in all the following tables are hypothetical and are used in 

 order to conform with those given in Clarke and Wheeler's manuscript. 



