302 THE ESSEX NATURALIST
varying concentrations. These concentrations were made up
by diluting sea water from Westcliff Sea Front (32.2 %0) with tap
water. Ten freshly collected specimens were placed in each dish
along with a small amount of substratum. The water in the
dishes was changed every two days, and every day where neces-
sary. The time of survival of each specimen was determined at
the different salinities and then the average time for survival
calculated. The results were then plotted and are shown in
figure 3.
Figure 3. The survival of C. arenarium in dilute seawater.