• ILLINOIS BIOLOGICAL MONOGRAPHS [200 



Mesostoma angidare nov. spec 74 



Mesostotna simplex nov. spec 77 



Family Gyratricidae 78 



Gyratrix hertnaphroditus Ehrenberg 1831 78 



Conclusions and Summary 81 



General discussion 81 



Summary 84 



Bibliography 85 



Explanation of Plates 88 



