FRESH WATER MUSSEL SHELLS 137 
DerpuctTioNs FrRoM TABLE OF PERCENTAGES. 
As the few shells of the series obtainable were quite old, it is 
difficult to come to any satisfactory conclusion concerning their rate 
of growth, and I have felt that the best insight is obtained by pre- 
senting the results as I have above. Within the limits of these 
observations, growth appears more rapid in the following dimensions, 
PD, AD, AHL, PHL, and TH. «It is relatively slower in L, DVD, 
DSD. Specimens may be larger at 10 years than some others at 
12 years. Increase in thickness is most marked. The rate of 
growth in PD, AD, AHL, PHL, is nearly the same. 
4 4. ELLIPTIO DILATATUS STERKII 
o. 
Spec. Age L DVD: DSD PD AD, °-PHE. AH. ie 
2 2.09cm. | cm. .5cm. 1.6 cm. .45cm. 1 cm. .3 cm..05cm. 
Bd 2a 95 - W329) AZ Gy N28 Gi 13% 150% 200% 
4 226% 243% 292% 229% 222% 240% 240% 380% 
5 246% .245% 300% 262% 206% 280% 273% 440% 
6) 21D 8) 235 9b 292 225 Ger VAIS 1237S 250G.. 38082 
8 342% 360% 450% 348% 300% 386% 350% 620% 
9 342% 355% .448% 368% 277% 396% 403% 480% 
10 370% 381% 480% 395% 260% 410% 423% 560% 
Il 385% 496% 570% 415% 313% 444% 433% 660% 
12 381% 374% 556% 407% 322% 440% 533% 600% 
veraze eroye per year in each dimension for 12 years, 
144% 160%. 219%. >. 156% 108% > 172% “AWG 85% 
Rees Ee ais 
DeEpucTIONS FROM TABLE OF PERCENTAGES AND REMARKS. 
' The greatest increase in the dimensions of this shell during the 
period indicated are to be found in DSD, PHL, AHL, and Th. 
Growth appears to be continuous through the years. PD and DVD 
increase at practically the same rate, while the increase in thickness 
is relatively large. Some of the shells are as large at 11 years as 
others are at 12. The rate of growth appears to be more rapid 
between the years 9-12 than years 4-8. This increase is not as well 
marked in AD as in other dimensions. 
Authors cited, (2), record a growth of 4.3 mm. for a medium sized 
specimen, (Unio gibbosus), in a crate anchored in the Mississippi 
river in a period a little over 2 years, 3 month, (p. 127). This 
amount of growth, which is a yearly average of 2.2 mm., is found 
in my specimens between the ages of 4-5, 8-9, 9-10, 11-12. 
