TABLE OF CONTENTS 



PAGE 



Introduction 7 



Polystomidae _ 9 



Historical Review of the Family 9 



The Genus Polystoma 16 



Anatomy and Histology of the Polystomidae 19 



Polystoma orbiculare Stunkard 1916 31 



Polystoma opacum Stunkard 1916 34 



Polystoma megacotyle Stunkard 1916 2>7 



Polystoma microcotyle Stunkard 1916 39 



Polystoma coronatum Leidy 1888 40 



Polystoma hassalli Goto 1899 42 



Polystoma ohlongum Wright 1879 44 



Key to the Species of the Genus Polystoma 46 



Aspidogastridae 47 



Aspidogaster conchicola von Baer 1827 48 



Cotylaspis insignis Leidy 1856 49 



Cotylaspis cokeri Barker and Parsons 1914 50 



Classification of the Family 57 



Paramphistomidae do 



Historical Review of the Family 60 



The Genus Alassostoma 64 



Alassostoma magnum Stunkard 1916 66 



Alassostoma parvum Stunkard 1916 69 



The Genus Zygocotyle 7 1 



Zygocotyie ceratosa Stunkard 1916 -2 



Classification of the Family _ 75 



Relation of the Families to the Order 80 



List of Xew Species 84 



Bibliography 85 



Explanation of Plates 91 



