546 
BULLETIN OF THE BUREAU OF FISHERIES 
Growth is clearly not isogonic. The young of both species are nearly round, but 
undergo a rapid change in shape as they grow, becoming greatly elongated. This 
reduction in width continues until the shell is about 5 centimeters in length, when 
S. patula has a width of about 36 per cent and S. alta a width of 42 per cent. During 
the remainder of the life of the clam the shell becomes wider until in the oldest 
specimens of S. patula the width measures 42 per cent of the length and in S. alta 
about 50 per cent. 
Treated by Huxley’s method of plotting the logarithm of the width on the 
logarithm of the length we obtain a consistent picture, k is at first less than unity 
(0.6) and gradually increases, reaching a value of 1 at five or six years (minimum of 
the above curve) and finally attaining a value of about 1.2. It will be noticed further 
that specimens from all parts of the coast have the same proportional width of shell. 
One exception is recorded: The largest shells from Pismo, Calif., show a tendency to 
be narrower than those from other localities. This difference, however, but slightly 
exceeds the probable error and is, therefore, of doubtful significance but may be 
interpreted as an effect of age on the proportional width. This would be comparable 
to our findings on sexual maturity, which occurs at essentially the same length on 
different parts of the coast, although at widely different ages (Weymouth, McMillin, 
and Holmes, 1925). Nevertheless a minor effect of age on sexual maturity can be 
traced, and it would be reasonable to expect a similar effect on relative width. 
Table 1 . — Average width of Siliqua patula from California, Washington, and Alaska, and of Siliqua 
alia from Alaska, for each centimeter of length 
Length in centimeters 
S. patula 
S. alta 
Alaskan 
Copalis 
Pismo 
100 W/L 
Number 
of speci- 
mens 
100 W/L 
Number 
of speci- 
mens 
100 W/L 
Number 
of speci- 
mens 
100 W/L 
Number 
of speci- 
mens 
17.0-17.2___ 
42.5 
2 
16.0-16.9 __ 
43.6 
14 
15.0-15.9 
42.9 
19 
43. 5 
2 
14.0-14.9 _ _ _ 
42. 1 
29 
43.3 
8 
13.0-13.9___ 
41.5 
21 
43.4 
28 
50.3 
12 
12.0-12.9 
41.0 
18 
41. 5 
34 
39.7 
23 
49.3 
62 
11.0-11.9 .... 
40. 5 
18 
41. 1 
37 
39.5 
36 
48.4 
31 
10.0-10.9 
39.9 
44 
40.3 
9 
39.0 
8 
49. 5 
16 
9. 0-9. 9 
38.8 
55 
38.2 
12 
37.8 
54 
49.3 
14 
8. 0-8. 9 
38.7 
31 
38. 1 
13 
38. 1 
33 
47.9 
15 
7. 0-7. 9 
36.9 
33 
37.5 
7 
38.0 
10 
47.2 
10 
6 0-6 9 
36.8 
21 
46. 5 
10 
5.0-5.9 
35.3 
12 
43.5 
17 
4. 0-4. 9 
35.3 
20 
37.3 
6 
42.2 
21 
3. 0-3.9 
36.0 
16 
35.8 
4 
43. 2 
9 
2. 0-2.9 
36.9 
33 
38.5 
8 
37.2 
38 
44.5 
7 
1. 5-1.9 _ _ _ _ _ _ _ 
41.0 
24 
41.0 
11 
41.9 
79 
1.0-1. 4 
43. 1 
101 
46.8 
17 
0. 5-0.9 
49.6 
67 
51.6 
14 
. 
51.0 
7 
0 3-0 4 
63.0 
12 
63. 2 
3 
0 1-0 2 
75.0 
7 
79.8 
3 
0.0-0 1 
89.6 
3 
71.0 
2 
