726 
BULLETIN OE THE BUREAU OF FISHERIES 
GMS 
100 
80 
60 
40 
20 
A 
LAM 
N0D0 
SSISSIP 
D SIL1S 
NT0ID 
PI RIVER 
"S - 
n 
M 
L. 
, IA. 
WEIGHT 
ON 
A 
GE 
- 
H 
■) 
1 
m 
0 
YRS. RINGS I 
n 
in 
IV 
v 
VI 
vn 
vm 
Figure 11— Bar graph showing weight plotted against age for individual left valves of shells of male yellow sand 
shells, Fairport, Iowa. Weight values of individual left valves indicated by black squares at right of year 
classes. Mean weight valves shown by striated squares to left of respective year classes 
Figure 12.— Bar graph showing weight plotted against age for individual left valves of shells of female yellow 
sand shells at Fairport, Iowa. Weight values of individual loft valves indicated by black squares at right 
of year classes. Mean weight values shown by striated squares to left of respective year classes 
