ANNUAL GROWTH OF FRESH-WATER MUSSELS 
733 
values for the mean weights are given in Table 12. It will be noticed that not only 
were the males longer for each year class than the females, but they also exceed the 
females in weight in those year classes for which data are available. 
CMS. 
50 
30 
10 
0 
50 
30 
10 
0 
YRS. RINGSVl 
vm 
LAMPSILIS 
SILIQUOIDEA PEPINENS1S 
CROSS LAKE. MINN. 
Figure 17. — Bar graph showing weight plotted against age for individual left valves 
of shells of male (above) and female (below) Lake Pepin mucket. Weight values 
of individual left valves indicated by black squares at right of year classes. Mean 
weight values shown by striated squares to left of respective year classes 
Table 12 . — Mean weight of left valves of Lake Pepin mucket, Lampsilis siliquoidea pepinensis, Baker, 
Cross Lake, Minn. 
Male 
Female 
Ring No. 
Number of 
specimens 
Weight 
Number of 
specimens 
Weight 
VI 
5 
Grams 
21.2 
11 
Grams 
19. 8 
VII 
9 
25.4 
19 
24. 3 
VIII 
14 
28. 1 
11 
25.9 
IX 
3 
39.6 
2 
32.3 
X 
2 
49.8 
2 
38.9 
Coker, Shira, Clark, and Howard (1921), held six specimens of this species at 
the United States Bureau of Fisheries Biological Station at Fairport, Iowa, for six 
years. The specimens were held in ponds freshly made at the start of the investiga- 
tions and kept filled with water pumped from the Mississippi River. The Fairport 
station is over 250 miles south of Lake Pepin which would give an appreciably longer 
and warmer growing season. The average length of these six specimens for each year 
compare very well with the lengths obtained for the Lake Pepin and Cross Lake 
specimens. After averaging the lengths for the two sexes for these last named lo- 
calities, and comparing the lengths for each age in the following order: Fairport, 
Lake Pepin, and Cross Lake, the figures for the second year are 4.34, 4.11, and 3.65 
centimeters respectively; for the third year, 6.88, 5.62, and 5.02; for the fourth year, 
7.70, 6.68, and 6.07; for the fifth year, 8.06, 7.40, and 6.88; for the sixth year, 8.49, 
7.95, and 7.47. Aside from the fact that so few specimens were available in the Fair- 
port tests, it is believed that they check up very well with what might be expected 
in relation to Lake Pepin and Cross Lake individuals. 
