Freshwater Mussels 235 
These authors point to the possible reduction of vitality in small 
lakes through inbreeding—hence less size. They also show that a given 
lake species reaches its maximum growth only in the more fluviatile 
lakes. The writer has often noted this inequality between the mussels 
of the isolated, headwater lakes such as Winona and those of the elong- 
ated, fluviatile Oswego and Tippecanoe lakes. 
Mussels are by no means unique in the occurrence of the smaller 
members of a family in smaller bodies of water, the larger members 
grading in size with the size of the stream or lake. Fishes are notable 
in this regard. 
MOVEMENTS AND MIGRATIONS. 
Isely (718) through the checking up of marked mussels arrived at 
the conclusion that well-grown river forms are virtually sedentary. Ever- 
mann and Clark (717) have often observed the tracks of mussels moving 
in shallow water. They state that the fixed habit increases with the 
increase in age and with increased depth. These observations are doubt- 
less true in spite of the seemingly anomalous fact that younger individ- 
uals burrow more deeply than the older. The limey crust on the former 
rarely covers more than the siphon region of the shell, indicating the 
extent of submergence. 
As told above, the writer has checked the movements of Winona 
Lake species, and finds an inshore or offshore movement corresponding 
to the stage of the lake water. 
Observations on White River in late spring, and after summer 
freshets, show that sand bars newly exposed after having been submerged 
for a time, are more or less populated. Furthermore, mussels are 
stranded sometimes by receding water, and often tracks are seen which 
show that an effort has been made to reach deeper water. 
Mussels upon rather permanent gravelly bars bounded by rock or 
mud bottom, are much limited in their movements. Shifting channels 
and shifting sand bars imply a corresponding movement of their popula- 
tion. 
During the summer of 1915 the writer marked sixty or more 
Lampsilis luteolus, somewhat after Isely’s method, and planted them at 
several points in the lake. Still others were planted during the follow- 
ing summer. Forty were put in water of three and one-half feet depth 
in Boys’ City Bay, on bottom of marly sand. In the summers of 1916, 
1917, 1919, and 1921 systematic efforts to recover these mussels were 
made. Many others of similar size were found, and many empty shells, 
but no marked mussels or shells were ever picked up. Others were put 
out in front of the Biological Station. Only two of these were.found sub- 
sequently. Three years later one was found that had moved fifty feet 
from the starting point and had shifted from water of two feet depth 
to four. The other record was about the same in distance without 
change in depth, in six years. In six years the latter had increased in 
length scarcely one-fourth inch. 
From the above it is clear that movements do take place. In some 
cases they are more or less seasonal, and of considerable magnitude 
deserving to be called migrations. 
