TABLE OF CONTENTS 



Introduction 7 



Methods of investigation 8 



Material 8 



Historical data 10 



Species previously described from North America 11 



New species described in this paper 12 



Families of Monostomidae 13 



Key to families 13 



Description of families 14 



Cyclocoelidae validity of the older name 14 



Diagnosis 14 



Key to subfamilies and genera 16 



Cyclocoelum 15 



Historical 16 



Structure of the genus 20 



Key to species of cyclocoelum 34 



Description of species 35 



Cyclocoelum leidyi nov. spec 35 



Cyclocoelum pseudomicrostomum nov. spec 37 



Cyclocoelum halli nov. spec 38 



Cyclocoelum wilsoni nov. spec 40 



Cyclocoelum cuneatum nov. spec 41 



Cyclocoelum obscurum (Leidy) 42 



Cyclocoelum macrorchis nov . spec 44 



Cyclocoelum triangularmn nov. spec 46 



Cyclocoelum vicarium (Arnsdorff) 47 



Notocotylidae 48 



Diagnosis of family 49 



Key to subfamilies and genera 49 



Notocotylinae 50 



Notocotylus 50 



Notocotylus urbanensis (Cort) 51 



Stages in the life history 52 



Notocotylm quinqueserialis (Barker and Laughlin) 53 



Catatropis 54 



Catatropis filamentis Barker 54 



Paramonostomum 55 



Paramonostomum echinum nov. spec 55 



Nudocotylinae 56 



Nudocotyle novicia Barker 56 



Heronimidae 57 



Heronimns chelydrae MacCallum 57 



CoUjTiclidae 60 



Collyriclum colei Ward 60 



Diagnosis 60 



Remarks on the life history 64 



