722 
Figure 8.— Median curve, together with first and ninth decil curves, of growth in length for 
both sexes of the yellow sand shell, Rio Grande Valley, near Mercedes, Tex. Maximum 
and minimum cases for the various year classes are represented by the locality symbol 
transfixed with a horizontal line 
Table 4. — Length in relation to age of yellow sand shell, Lampsilis anodontoides (Lea), Rio Grande 
Valley, Tex. 
fAll values in centimeters] 
MALE 
Ring No. 
Minimum 
First decil 
Median 
Ninth decil 
Maximum 
I_ 
3.2 
3. 52±0. 0944 
4. 61±0. 1079 
5. 69±0. 0944 
6.4 
II _ 
5.6 
6. 76± . 2496 
8. 02± . 1052 
9.09± .0944 
9.6 
III.. 
8.0 
8.99± .0951 
10. 11± . 1072 
11.03=1= .0405 
12.0 
IV__ 
10.4 
10. 67± .1103 
11.21± .0832 
11.85=1= .8863 
12.6 
V.... 
11.2 
11.32± .2496 
12.00± .3932 
12. 88± . 1568 
12.8 
VI 
i 12.54 
i 13. 97 
FEMALE 
3.4 
6.0 
9.0 
9.8 
3. 91±0. 1710 
7. 72± . 1001 
9. 36± . 1685 
9.90± .4519 
4. 80±0. 1428 
8. 33± . 1320 
10. 20± . 1832 
12. 10± . 1130 
i 13. 00 
i 13. 03 
6. 14±0. 1710 
10.84± .1710 
12. 60± . 2964 
13.50± .4519 
7.4 
11.0 
12.8 
13.4 
1 One individual. 
Returning to Figure 5, which contains the median curves for increase in length 
for the species as found in all three localities, the differences in rate of increase in 
length become apparent. The actual values are given in Table 4. The essential 
difference lies in the fact that in the most southern of the three localities, the Rio 
