CHEMISTRY: CLARKE AND STEIGER 
la 
lb 
2a 
2b 
3a 
3b 
Si02+(Al,Fe)203 
0.33 
0.35 
0.36 
0.66 
0.31 
0.57 
10.81 
1 74- 
1 1 98 
8 1 9 
in 00 
o . / / 
CaCOs 
72.41 
78.98 
55.46 
70.58 
56.89 
65.14 
CaS04 
1.24 
1.23 
2.12 
1.58 
2.32 
2.32 
Ca3P208 
15.21 
11.70 
30.78 
19.06 
29.49 
23.20 
100.00 
100.00 
100.00 
100.00 
100.00 
100.00 
In each case the claw is richer in magnesium carbonate and calcium phos- 
phate than the carapace. The variations due to age appear more distinctly 
when the average of each pair of analyses is taken, as follows: 
1 
2 
3 
MgCOs 
9.27 
9.70 
9.88 
CaCOs 
75.69 
68.02 
61.01 
CagPsOg 
13.45 
24.92 
26.35 
CaS04 
1.24 
1.85 
2.32 ' 
Here the progressive increase in magnesium carbonate and calcium phos- 
phate is clearly shown; and it also appears in the percentages of calcium 
sulphate, although the last detail is less significant. The smallest lobster, 
moreover, differs in the composition of its inorganic portion from that of the 
two larger animals much more than they do from each other. 
From the evidence now at hand it seems clear that some of the departures 
from regularity in the proportions of magnesium carbonate in the shells or 
skeletons of marine invertebrates are due to one or both of the two causes 
which were suggested at the beginning of this paper. It is desirable, there- 
fore, in further investigations of this kind, that in the study of the more 
highly specialized organisms the analyses should represent the totality of the 
inorganic portions, and that animals of the same degree of maturity should be 
taken. With the lower classes of organisms the difficulties are not so great, 
and regularities are much more easily discovered. 
(PubHshed by permission of the Director of the U. S. Geological Survey.) 
1 Clarke and Wheeler, Prof. Paper, No. 102, U. S. Geological Survey, Washington. 
