142 THE AMERICAN MIDLAND NATURALIST 
and its rate of growth has been studied in: greater detail than in 
any other mussel. Coker, Shira, Howard and Clark, (2), record 
its growth as follows, p. 126. 
Age Length % Increase 
2 43.4mm. 
3 z 68.8mm. 158% 
+ 77 mm. « 177% 
5 80.6mm. 180% 
6 84.9 , 170% 
Howard, (9), p. 70, records even a greater average increase in 
length from mussels reared in a floating crate—209%. My youngest 
L. Erie specimen was 6 years old and had a length of 51.2 mm. 
against 84.6 mm. for those from the Upper Mississippi River. 
However, it is well’ known that the lake forms of this species, as 
will be taken up in detail later, are unusually depauperate when 
compared with those from the Mississippi. The average rate of 
growth calculated from their data is 62%, while between the years 
6 and 7, I record a minimum of 82%. 
12. LAMPSILIS OVATA CANADENSIS 
No. 
Spec. Age L DVD PSD aie» AD> PH Anion semble 
z 4 1. 9cm. 1.29cem. .74cm. 1.28cm. 1.22cm.  .67cm. .42cm..12cm. 
2 7 332% 339% 400% 336% 164% 400% 352% 183% 
2 8 ~272% 216% 332% ~273% 137% 310% 305%. 133% 
4 9 317% 360% 480% 479% 155% 388% 326% 208% 
+ 10 340% 372% 425% 343% 152% 417% 262% 191% 
4 Il 350% 400% 423% 365% 170% 440% 356% 250% 
4 12 423% 466% 509% 453% 190% 552% 373% 291% 
4 13 378% 390% 463% 406% 163% 485% 395% 300% 
4 14 418% 461% 520% 453% 173% 522% 380% 308% 
4 15 426% 482% 573% 484% 178% 609% 440% 333% 
4 16 460% 509% 556% 476% 212% 606% 440% 308% 
I 17 503% 527% 635% 541% 210%  °+716% 416% 350% 
I 19 515%. 529% 623% 586% 188%. 619% 511% 366% 
Average growth per year in each dimension for 19 years, 
186% | 206% 249% 210% 47% 256% 187% 106% 
DrpuctTions FRoM TABLE oF PERCENTAGES AND REMARKS. 
The average increase is most marked in the dimensions of DVD, 
DSD, PD, PHL, growth in AD being less. Growth appears to be 
somewhat irregular, some specimens being larger at an early age 
than others. J'H increases consistently with age, and the rate of 
growth of DSD, TH, and PHL is most similar. Growth appears to 
be greater m years, (7-11), than in later ones, (12-16). During the 
latter period, however, growth in thickness is most rapid, PHL 
markedly more, dD, L, and AHL relatively less, 
