ANNUAL GROWTH OF FRESH-WATER MUSSELS 
725 
Table 6.- — Annual increase in length of yellow sand shell 
Year ring 
Locality and increase 
III 
IV 
VI 
VII 
VIII 
MISSISSIPPI RIVER, IOWA 
Cms. 
Cms. 
Cms. 
Cms. 
Cms. 
Cms. 
Cms. 
Cms. 
Male, annual increase 
Female, annual increase. 
Male, cumulative increase Irom first year.. 
Female, cumulative increase from first year. 
1.61 
1.58 
3.93 
3.59 
3. 93 
3. 59 
2.68 
3. 30 
6. 61 
6. 89 
1.35 
1.49 
7. 86 
8. 38 
0. 81 
.87 
8. 77 
9. 25 
0. 92 
.67 
9.69 
9. 92 
0.60 
. 40 0. 40 
10.29 
10. 32 10. 72 
WHITE RIVER, ARK. 
Male, annual increase 
Female, annual increase 
Male, cumulative increase from first year... 
Female, cumulative increase from first year. 
2. 80 
3. 35 
3.89 
3.58 
3.89 
3. 58 
2. 24 
2.20 
6. 13 
5.78 
1.33 
1.30 
7. 46 
7.08 
1.24 
.54 
8.70 
7.62 
.60 
.43 
9. 30 
8. 05 
.10 
9.40 
1.10 
10.’ 50 
RIO GRANDE VALLEY, TEX. 
Male, annual increase 
Female, annual increase 
Male, cumulative increase from first year___ 
Female, cumulative increase from first year. 
4.61 
4.80 
3.41 
3.53 
3. 41 
3.53 
2.09 
1.87 
5.50 
5. 40 
1. 10 
1.90 
6.60 
7. 30 
.79 
.90 
7. 39 
8. 20 
1.26 
.63 
8. 65 
8. 82 
CMS 
Figure 10.— Mean weight of left valves for year classes of yellow sand shell, Mississippi River, Fairport, 
Iowa; White River, Newport, Ark.; and the Rio Grande Valley near Mercedes, Tex. Weight plotted 
against age 
WEIGHT IN RELATION TO AGE 
Figure 10 shows the mean weights for the different year classes of the left valves 
of both sexes of the yellow sand shell from the three localities. Actual values are 
given in Table 7. Since only a single weight was taken from each valve, while 
several length values may be taken, there is a much more limited range to the weight 
values than to the length values. However the weight values obtained seem suffi- 
cient to indicate the essential differences in annual weight gains made by this species 
in the three localities. 
