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PACIFIC SCIENCE, VoL XX, April 1966 
Fig. 1. Map showing approximate position of col- 
lecting localities. 
Individual analyses of Na in D. excentricus 
tests ranged from 3,800 to 12,200 ppm, averag- 
ing 6,440. Mean values of three tests from each 
locality range from 4,100 to 10,600 ppm. Very 
few analyses of Na in the skeletons of other 
organisms are available for comparison with 
these data. The low-Mg calcite shells of the 
common oyster, Crassostrea virginica, generally 
contain between 2,000 and 3,000 ppm Na, 
which is somewhat lower than that observed in 
high-Mg calcite sand dollar tests. A direct re- 
lationship between the Na content and salinity 
was observed in oyster shells by Rucker and 
Valentine (1961), but this was not observed 
in sand dollars (Fig. 2 ) ; however, the oysters 
were collected over a much wider range of 
salinities. 
The Mn content of D. excentricus tests range 
from 12 to 91 ppm and averages 35 ppm. The 
average concentration of the three tests from 
each locality ranges from 13 to 84 ppm. Figure 
2 shows that the lowest values of Mn are 
found in tests from cold waters; the cold-water 
tests also exhibit the greatest variation in Mn 
content. Salinity does not appear to affect the 
Mn content consistently. Judging from the few 
published figures on Mn in organic carbonate 
materials, the high-Mg calcite skeleton of 
D. excentricus contains Mn in intermediate 
amounts, i.e., lower than some figures reported 
for low-Mg calcite skeletons, higher than those 
reported for some aragonite skeletons (Rucker 
and Valentine, 1961; Pilkey and Goodell, 
1963). 
The Fe content of D. excentricus tests ranges 
from 140 to 620 ppm and averages 270 ppm. 
Location averages range from 187 to 573 ppm. 
Again, no strong temperature or salinity effect 
is apparent (Fig. 2). The concentration level 
of Fe in D. excentricus tests is similar to that 
noted in both low-Mg calcite and aragonitic 
skeletons of other organisms. 
MEAN SUMMER WATER TEMPERATURE (°C) 
Fig. 2. The relationships between concentration of 
elements and mean summer water temperature. 
