218 
BULLETIN OF THE BUEEAU OF FISHEEIES 
GROWTH IN DIFFERENT LOCALITIES 
Many shells of various localities have been examined and the total length of 
each ring determined, thus giving a great mass of records of lengths at known ages. 
All measurements were made with one caliper by one or two persons. The caliper 
was graduated in millimeters, and by the use of a vernier scale could be read to 
tenths of millimeters. While all measurements were made and recorded in tenths 
of millimeters, the last place was not used in calculations. A few measurements 
were made in the field, but the majority were made in the laboratory. There is 
0 I 2 3 4 S b 7 8 9 to II 12 13 H 
Aae IN Years 
Fig. 14. — Showing the growth of clams from three localities. From this the average size for any 
age can be read. For example, the lengths for 3 years of age are as follows : Cordova, 4.61 
centimeters (1% inches) ; Swickshak, 6.41 centimeters (2^^ inches) ; and Washington, 10.87 
centimeters (414 inches). The legend of the abscissa "age in years", is used for convenience. 
The age rings form first at % year of age, and annually thereafter. Therefore, the actual age 
is % year less than indicated on the graph 
usually a change in density or pigmentation of the shell at the annual ring. The 
use of light to make these zones more apparent was found to be very helpful. If 
a shell is exposed to direct sunlight or a strong arc or incandescent light is placed 
under it, the annual rings show up in such a way that they can be measured with- 
out difficulty. 
From measurements made in this manner growth curves for clams from 
various beaches have been constructed. Three curves presented here (fig. 14) were 
made from clams taken from beds at Copalis, Wash., and Cordova and Swickshak, 
Alaska. The data are given in tables 1 to 4, inclusive. 
