MUSSELS OF WINONA, PIKE, AND CENTER LAKES. 



307 



specimens found were taken on sand and gravel and white marl 

 bottoms in from four to twenty-two feet. 



FIG. I. Map of Winona Lake showing mussel beds. = U. luteolns light 

 variety; = U. luteolus dark variety; =A. grandis; </> =- A. edentula ; 



- U. rubigiti osus ; S = U. subrostratus. 



There are a number of conditions which suggested themselves 

 as possible explanations for this distribution sex, light, temper- 

 ature, food supply and oxygen, pressure, wave action, character 

 of the bottom, and enemies. Sex cannot be important, for males 

 and females are found together throughout the habitat ; light can 

 have but little to do with it, for mussels are absent in places in 

 three feet of water and are abundant in others in fifteen feet, the 

 difference in light being considerable. Further, the light over 

 some of the immense beds in White River is no greater and per- 

 haps even less than in twelve feet of lake water. That heat and 

 cold have little effect, during the summer at least, is shown by 



