ANNUAL GROWTH OF FRESH-WATER MUSSELS 
721 
until the fourth year. Thereafter, a marked divergence appears for the fifth and 
sixth years. Unlike the Mississippi River shells, the Arkansas males have the greater 
rate of growth in length. No specimens of females of more than 6 years of age were 
available in the Arkansas collection, which was unfortunate, as the marked drop in 
length increase for the males in the seventh year suggests that the trend of the two 
sexes might be toward each other, as in the case of the Mississippi shells, although 
the location of the 8-year class suggests a new trend for the males in extreme age. 
Table 3 .—Length in relation to age of yellow sand shell, Lampilis anodonioides {Lea), White 
River, Ark. 
[All values in centimeters! 
MALE 
Ring No. 
Minimum 
First decil 
Median 
Ninth decil 
Maximum 
I__ 
1.0 
1. 27±0. 1192 
2. 80±0. 2012 
4. 60±0. 1589 
5.0 
II 
4.4 
5. 20± . 1589 
6. 69± . 1255 
7.80± . 1192 
8.0 
III 
7.2 
7. 90± . 1275 
8. 93± .0767 
10. 10± . 1594 
11.0 
IV 
8.6 
9. 64± . 1102 
10. 26± .0970 
10. 88± . 1983 
11. 6 
V 
10.8 
10. 94± . 1776 
11. 50± . 1489 
11.86=t . 1332 
11.8 
VI 
11. 6 
1 1. 08± . 1349 
12. 10± . 1686 
12. 52± . 1349 
12. 4 
VII __ 
12.0 
12. 08± . 1398 
12.2 ± .4497 
13. 52± .4195 
13.4 
VIII 
■ 12.6 
• 14.0 
FEMALE 
I_ 
0. 6 
1. 88±0. 1589 
3. 35 ±0. 1703 
4. 85±0. 1430 
5.2 
II. 
4.4 
5. 27± . 1787 
6. 93± . 1135 
7. 78± .0670 
8.4 
III 
6.8 
8.26± .1342 
9. 13± .1389 
10. 27rb . 1175 
10.8 
IV 
8.2 
9. 66± .0726 
10. 43± .0878 
10. 99± .0715 
11.2 
V 
9. 6 
10. 13± . 0987 
10. 97± . 1067 
11. 61± . 1207 
12.0 
VI _ 
10.6 
10. 22± . 4047 
11.40± .3373 
12.32± .4047 
12.2 
1 One individual. 
Coker, Shira, Clark, and Howard (1921), give some figures on the lengths of 
40 specimens of yellow sand shell from the St. Francis River, Ark., which they 
studied. Ages were determined from the growth rings. Their figures are of in- 
terest in comparison with those obtained in these studies. They state that they 
found 3-year-old specimens about 4 inches (10.16 centimeters) long. This compares 
with the median length for the White River shells, averaging males and females, 
obtained in these studies of 9.03 centimeters. Four-year-old specimens, they state, 
were 4 to 4 % inches (10.16 to 11.43 centimeters). The corresponding figure in these 
studies is 10.35 centimeters. For 5-year shells they give no figure, but 5-inch (12.7 
centimeters) shells, they state, are 6 or more years of age. The median length of 
the 6-year-old shells from the White River is 11.75 centimeters. 
In Figure 8 the curves of growth in length for the specimens from the lower 
Rio Grande Valley may be seen. 
In the lower Rio Grande Valley the growth in length during the first year is 
very great, but thereafter there is a decline in the growth rate. The sexes diverge 
in rate after the third year, with a marked separation the following year. There 
is a suggestion that the curves for the sexes tend to approach each other after the 
fifth year, but since only one female over 4 years old was available, this can not be 
established definitely with the material at hand. 
