CONTENTS. 



Page. 



Introduction 5 



Glacial origin of lakes and rivers 6 



Mussels of the St. Croix group 8 



Mussels of the Minnesota River group 11 



Mussels of the Red River group 11 



Mussels of the Crow Wing group 14 



Mussels of the Mississippi group 17 



Mussels of the isolated lakes 20 



Summary 25 



3 



