Freshwater Mussels 229 
WALNUT 
AA 
DICKEY'S 
SUBS 
io 
in POCAH ONTAS 
Fig. 1. Winona Lake, Indiana. Ten and twenty-foot contours shown. Letters rep- 
resent stations referred to in text. Arrows are shore currents. 
hence a slow distribution of its mud toward Boys’ City Bay (Scott, 716, 
p. 14, map) and a rather firm bottom results. 
The terrace constitutes a shelf of rather moderate depth surround- 
ing the lake. This is the principal habitat of the mussel population. 
Baker (’16) and others have recorded the occurrence of the maximum 
population on the most exposed points of the shores of lakes. This 
generalization holds for Winona Lake except at its extreme leeward cor- 
ner—Boys’ City Bay—where the drift, marl, and mud from all parts of 
the lake accumulate and are graded out within a short distance from the 
shore. Kosciusko beach (Map, B) is the most exposed part of the shore 
line. Here in spite of much intensive collecting it continues to be one of 
the most populous areas of the lake bottom. 
FACTORS GOVERNING DISTRIBUTION IN WINONA LAKE. 
Having in mind the character of the lake it will now be pertinent 
to examine the facts of distribution and the possible factors limiting the 
same. We will first consider the three accepted by Headlee and Simon- 
ton. 
(1) Muskrats. These animals are known to depopulate small areas 
of mussel beds. Where occurring in sufficient number it is possible that 
they very definitely limit the shoreward extension of the same. However 
at the present time there are too few muskrats here to have a signifi- 
cant effect, except locally, about the mouths of creeks in particular. 
