VI 



PAGE. 



Nymphs 25 



Imagos 26 



Family Petalurida 27 



Fatiitly .'EscJuiidcE 27 



Key to Genera 30 



Imagos 30 



Nymphs 32 



Nasiasschna 33 



Epiaeschna 35 



Boyeria 36 



Basiaischna 38 



yEschna 39 



Key to nymphs 40 



Anax 46 



Family Gomphidce 50 



Keys to Genera 52 



Imagos 52 



Nymphs 53 



Aphylla 54 



Progomphus 55 



Diastatatomma and Herpetogomphus 57 



Key to nymphs 58 



Hagenius 60 



Lanthus 62 



Dromogomphus 64 



Gomphus 65 



Key to nymphs 66 



Species 68 



Literatuie go 



ARTICLE II. -PLANKTON STUDIES. IV. THE PLANKTON OF 

 THE ILLINOIS RIVER, 1894-1899. WITH INTRODUCTORY 

 NOTES UPON THE HYDROGRAPHY OF THE ILLINOIS 

 RIVER AND ITS BASIN. PART I. QUANTITATIVE INVES- page 

 TIGATIONS AND GENERAL RESULTS. BY C. A. KOFOID.... 95 629 



Introduction 



95 



Acknowledgments 96 



The Geological and Hydrographic Features of the Illinois 



River Basin 98-251 



Introdiictoty gg 



Location oq 



Geological Features of the Illitiois River Basin 99 



Elevation qg 



Glacial and valley Drift 100 



Relief loi 



T/ie Illinois River System 102 



Length and area 102 



