732 
BULLETIN OF THE BUREAU OF FISHERIES 
Table 11 . — Length in relation to age of Lake Pepin mucket, Lampsilis siliquoidea pepinensis, Baker, 
Cross Lake, Minn. 
[All values in centimeters] 
MALE 

Ring No. 
Number of 
specimens 
Minimum 
First decil 
Median 
Ninth deoil 
Maximum 
I 
100 
1.0 
1.42 ± 
0. 0519 
2.25 =b 
0. 0648 
2.96 rb 
0. 0506 
3.4 
II 
100 
2.4 
3.02 rb 
. 0613 
3.88 rb 
.0609 
4. 54 rb 
.0533 
5. 0 
HI _ 
100 
3.4 
4.36 rb 
.0843 
5. 11 rb 
.0527 
5.90 rb 
.0675 
6.2 
IV 
100 
4.6 
5.47 rb 
.0749 
6.17 rb 
. 0581 
6.90 rb 
.0636 
7.8 
V 
100 
5.8 
6.25 rb 
.0613 
7.09 rb 
.0489 
7.65 rb 
.0519 
8.4 
vi 
97 
6.6 
7. 12 =b 
.0452 
7.69 rb 
.0500 
8.38 rb 
.0497 
9.0 
Vli 
85 
7.2 
7.68 ± 
.0443 
8.21 rb 
.0525 
8.94 rb 
.0601 
9.2 
Vlil 
60 
7.4 
8.09 rb 
.0742 
8. 72 rb 
. 1221 
9.35 rb 
.0616 
9.8 
IX . 
33 
8.2 
8.46 ± 
.0725 
9.01 rb 
.0742 
9.39 rb 
.0609 
9.8 
X 
10 
8.8 
9.00 ± 
.0713 
9.32 rb 
. 1180 
9.80 rb 
.0624 
9.8 
XI 
4 
9.2 
9.28 ± 
. 1349 
9. 70 =b 
. 1686 
9.92 ± 
.1349 
9.8 
XII 
1 
9. 81 
FEMALE 
I 
100 
1.0 
1.34 rb 
0. 0637 
1.98 rb 
0. 0511 
2. 60 rb 
0. 0431 
3.0 
II 
100 
2.4 
2.90 rb 
.0413 
3. 42 rb 
.0535 
4.42 rb 
. 1920 
5. 0 
HI 
100 
3.2 
4.22 rb 
.0637 
4.93 ± 
.0535 
5.71 rb 
.0749 
6.4 
IV 
100 
4.2 
5.23 rb 
. 0612 
5.96 rb 
.0508 
6.72 rb 
. 0685 
7.4 
V 
100 
5.4 
6.03 rb 
.0595 
6. 67 rb 
.0456 
7.31 rb 
.0505 
8.0 
vi _ 
100 
6.0 
6.68 rb 
.0460 
7.24 rb 
.0475 
7.89 rb 
.0723 
8.4 
VII 
73 
6.6 
7.01 ± 
.0443 
7.56 ± 
.0564 
8. 16 rb 
.0523 
8.8 
VIII 
32 
7.0 
7.44 ± 
.0637 
7.87 ± 
.0723 
8.56 rb 
.0882 
9.0 
IX 
12 
7.8 
7.85 ± 
. 1123 
8.40 rb 
.1938 
8.65 rb 
.0843 
8.8 
X 
2 
8.11 
8. 55 
8. 98 
The growth curves of the Pepin mucket are of the same general type as those of 
the yellow sand shell, of the buckhorn, and of Pope’s purple, the major differences 
between these several curves being those of rate — the Pepin mucket having an appre- 
ciably slower rate of growth than its congener, the yellow sand shell. The year 
classes in the curves of the Pepin mucket, however, are quite suggestive in comparison 
with the curves of the yellow sand shell. Although no selection of individuals was 
made when the original collections were obtained, the year classes in the yellow 
sand shell groups include only the VUI-year class, with most of the individuals 
dropping out at the Vl-year class, while the year classes of the Pepin mucket groups 
include the XHI-year class, with a good representation in the X and XI year classes. 
Shelters along the river regularly report that they do not find “mossbacks” and 
“old-timers” among the yellow sand shells as they do among the Pepin muckets, 
and examinations of various heaps of unsorted shells as collected from the river 
verify these statements in that yellow sand shells more than 6 years old are hard to 
find. No explanation of these differences in the apparent lengths of the life spans 
of the Pepin mucket and yellow sand shells is offered ; but of the four species studied, 
the two slow-growing species, the Pepin mucket and the buckhorn, are both well 
represented in the higher year classes — that is, those above the Yl-year class. 
Within the species, the Pepin muckets from Lake Pepin show a slightly greater 
rate of growth in length than the Pepin muckets from Cross Lake. Several factors 
may combine to produce this difference, but it may be pointed out that Cross Lake 
is farther north, and that the ice is known to remain in this lake much later in the 
spring than in the Mississippi at Lake Pepin. 
Figure 17 shows the distribution of the left valves of the Cross Lake shells in the 
different year classes according to weight, males in the upper portion of the chart, and 
females in the lower portion. Each black square represents one left valve. The 
mean weight for each class is indicated by the squares with diagonal lines. Actual 
