720 
BULLETIN OF THE BUREAU OF FISHERIES 
Figure 5 shows the median curves of growth in terms of length for the yellow 
sand shell as found in all three localities; and Figure 6 the growth curves for each 
sex of this species from the Mississippi River. It will be noted from Figure 6 that 
length of the individuals from the Mississippi increases very rapidly through the 
second year, after which a decrease in the growth rate sets in, becoming pronounced 
the fourth year. This rapid growth appears associated with the mussel’s juvenile 
period, and with the coming of maturity, in the third season, the rate of increase in 
length steadily decreases. There is some difference in the rate of increase in length 
between the sexes. After the formation of the second annual ring the females take 
Figure 7. — Median curve, together with first and ninth decil curves, of growth in length for both sexes of 
yellow sand shell, Lampsilis anodontoides (Lea), White River, Newport, Ark. Maximum and minimum 
cases for various year classes are represented by locality symbol transfixed by a horizontal line 
the lead in growth over the males, which up to this time have grown faster. This 
lead remains definite until the seventh year, when there is an indication of a mutual 
drawing together of the curves of growth in length of the two sexes. The males 
increase in rate, while the females decrease. The fact that the females do not grow 
quite as rapidly as the males the second year but more rapidly the third year sug- 
gests that the females do not reach maturity the second year, in as great a proportion 
at least, as the males. All, or a greater proportion, of the females appear to mature 
a year later than the males. 
Figure 7 gives the curves of growth in length for the individuals found in the 
White River of Arkansas. As with the Mississippi shells, length increases most 
rapidly during the first and second years, after which a steady decrease in rate of 
growth sets in. The rates of increase in length for the two sexes remain close together 
