FRESH WATER MUSSEL SHELLS 141 
grow largely at the same rate. It is observed that some specimens 
are as large at 14 as at 18 years. 
The preceding observations are based largely on the averages, but 
a comparison of from age to age of the above percentages indicates 
that DSD increases steadily throughout, as well.as PHL and PD: 
AD seems to relatively diminish with the years, while in later ones, 
PD, DVD, and DSD tend to increase relatively more rapidly than 
the length. The rate of growth of the hinge lines is approximately 
the same. Certain specimens reach a maximum growth earlier than 
others. 
Of the 19 species of Unionidae studied by authors cited, (2), the 
greatest growth for a period a little over 2 years, 3 months, was 
observed in a medium sized example of this species. The gain in 
that period was 44.7 mm. in one specimen alone, a yearly average 
of 2.23 cm. Referring to my data, I find even a greater growth 
between the ages of 9-10, 11-12, 15-16. 
11. LAMPSILIS (LUTEOLA) SILIQUOIDEA ROSACEA. 
No. ~ 
Spec. Age 1 DVD DSD PD AD eerie AHL TH. 
Gu oeliZemno em) 1-o5em= Se4ocnIs 3cm. 2.35cm. | cm. .20cm. 
4 
te 
2 7 “110% 108% 74% 108% 115% 119% 112% 130% 
2 Semone: 110% ) Hes 102% IT Ze 12330 22% 2 12082 
2 Seite c 120% « 120 Ge ns GZ ISS 8 Bon 22Z Be aoe 
3 10 134% 136% 146% 142% 137% 144% 196% 160% 
3 11. 142% 140% 151% 147% 128% 162% 156% 170% 
3 12 155% 151% 265% 160% 146% 171% 190% 210% 
3 13. 107% 119% 117% 126% 108% 119% 156% 251% 
3} 14 161% 154% 171% 166% 147% 183% 163% 180% 
3 15 144% 143% 148% 150% 130% 181% 156% 190% 
3 16. 147% 135%. 186% »=185% 123% — 175%. 158%. | 175] 
2 17 167% 155% 172% 171% 158% 204% 180% 210% 
2 18* 152% 148% 176% 158% 146% 180% 178% 215% 
1 19 167% 158% 164% 171% 161% 172% 185% 170% 
Average growth per year in each dimension for 19 years, 
6% 25% 42% 32% 21% 41% 40% 54% 
DepucTIons FROM TABLE OF PERCENTAGES AND Remarks. 
Throughout the life of the animal, as illustrated in the above 
series, growth is most rapid in DSD, PD, PHL, AHL and in TH. 
Specimens may be as large at 17 years as at 19. Thickness exhibits 
the most outstanding increase. According to these results, the shell 
grows somewhat more rapidly after twelve years than in the six 
preceding ones, the thickness nearly doubling. L, D/D, DSD grow 
largely at the same rate. 
This species of mussel is of considerable commercial importance, 
