554 
BULLETIN OF THE BUREAU OF FISHERIES 
first but with an increasing slope up to a certain point, followed by a decreasing 
slope during the remainder of the curve. This inflection, or point of change from in- 
creasing to decreasing slope was not noticed in our early growth studies on the Wash- 
ington beds. Ultimately a method of fitting, to be discussed later, convinced us 
Figure 5.— Growth curves from seven localities in California, Oregon, British Columbia, and Alaska. Ages are indicated 
by ring number; to determine actual age subtract one-half year 
that an inflection is present in all, and the curves of absolute growth have been so 
drawn. The inflection, on the average, is at 22.36 per cent of the maximum age 
and 32.75 per cent of the total length. There is no obvious correlation between these 
ages and lengths and any other features of the growth curves as maximum age, maxi- 
mum length, relative growth rate, or 
the like. 
Following the inflection, the rate 
of growth decreases regularly until a 
final adult length characteristic of the 
locality is reached. This varies from 
12 to 16 centimeters, the slower-grow- 
ing northern clams reaching in general 
the greatest size and having the 
longest life. 
To show the rate of absolute 
growth we may plot the annual in- 
crements, or differences between suc- 
cessive total lengths, on the age. (Fig. 
7.) This shows an increase of rate 
which reaches a maximum at the point 
of inflection of the total length 
curve. This maximum may fall early 
in life; and, since the smallest time in- 
terval available is the year, its location may only be approximated by this method. 
Following the maximum, the rate declines throughout life and for a time closely 
approximates a descending geometric series; that is to say, each yearly growth is a 
certain percentage of the preceding. This relation was first pointed out by Putter 
<AgE (TEARS ) 
Figure 6. — Growth curves for three localities in Washington. Ages 
are indicated by ring number; to determine actual age subtract 
one-half year 
