AGE AND GROWTH OF THE PACIFIC COCKLE 
637 
time. As shown by Weymouth, McMillin, and Rich (1931) and by Weymouth and 
McMillin (1931), this decline closely approximates an exponential series, so that the 
log of the relative growth rates plotted on age gives a straight line. 
If relative growth rate = ^ ^ ^ = P L , then 
log P L = a — kt 
P L = e a ~ kt 
P L = Ae~ kt 
where A = e a 
dl °S L ==Ap -u 
dt Ae 
log L = e~ ktJ r ' 
log L = b — ce~ kt 
where c = ^- 
L = e t,-ce- kt 
L = Be~ ce 
where B = e b 
Table 1 is a comparison of the observed lengths of Cardium corbis with the lengths 
calculated by the formula L = Be~ ce ~ kt , developed by Weymouth, McMillin, and 
Rich (1930), and Weymouth and McMillin (1930). 
Table 1 . — Comparison of observed and calculated lengths of Cardium corbis 
SNUG HARBOR 
Year 
N 
L 0 
L 0 
Lo— L„ 
P.E.o 
Year 
N 
Lo 
L„ 
L 0 — Lo 
P.E.„ 
1 
1 
7 
7 
6 
6 
0.34 
1.09 
2. 92 
4. 96 
6. 54 
0. 363 
1. 280 
3. 040 
4.949 
6. 511 
-0. 023 
-.190 
-. 120 
.011 
.029 
6 
6 
6 
6 
3 
2 
7.52 
8.27 
8. 75 
8. 95 
9. 09 
7. 599 
8. 289 
8. 705 
8.949 
9. 089 
-0. 079 
-.019 
.045 
.001 
.001 
0. 2135 
.2164 
.4340 
2 
0. 5018 
.2394 
.5281 
.2972 
7 
3 
8 
4 
9 
5--. 
10 
Note. — N=numb<;r of individuals; L 0 =observed lengths; P.E. 0 =probable error of observed lengths; and L 0 = calculated 
_ f. § _(! 247345 
lengths: L=Be~ ee , L= 9.27228e 6,2473154 
GROWTH IN DIFFERENT LOCALITIES 
The three curves presented in Figure 7 show the marked variation in the growth 
of the species in different localities. These have been constructed from measurements 
of clams taken on the beds of Copalis, Wash., and Kake and Kukak Bay, Alaska. 
In general, it may be said that Cardium corbis, in the southern part of its range, makes 
a tremendous early growth, with which is associated a short life and a small size. 
The northern forms show a low initial growth rate, a long life, and a larger size than 
that attained by the southern forms. Insufficient growth data for the more southern 
forms have made it impossible to plot the course of their growth. However, where 
data have been obtained the growth resembles that of the Copalis cockle. 
The growth of Cardium corbis is an interesting confirmation of the conclusions 
reached by Weymouth, McMillin, and Rich (1930) in regard to the growth of the 
