TABLE OF CONTENTS 



Introduction 7 



Acknowledgments 8 



Physical Features of the Big Vermilion Basin 10 



General Biology of the Big Vermilion River 15 



Plants 15 



Worms 15 



Crustacea 16 



Aquatic Insects 16 



Higher Vertebrates 18 



Fish Fauna of the Big Vermilion River 18 



General Distribution of the Mollusk Fauna 24 



Ecological Variation 25 



Comparisons with Other River Systems 28 



Systematic Discussion of the Mollusca 31 



Unionidae 31 



Sphaeriidae 58 



Pleuroceridae 59 



Amnicolidae 60 



Viviparidae 61 



Ancylidae ... 63 



Physidae 64 



Planorbidae 64 



Lymnaeidae 65 



Pollution of the Salt Fork by Sewage and Manufacturing Wastes 67 



General Nature of Stream Pollution 67 



Sewage Pollution in the Salt Fork 72 



Recent Examination of the Polluted Portion of Salt Fork 80 



Summary of Salt Fork Conditions 88 



Summary and Conclusions 90 



Unfavorable Influences 90 



Parasites and Pathologic Agencies 91 



Economic Considerations 91 



Bibliography 94 



Explanation of Plates 97 



