CONTENTS 



PAOE 



Introduction 327 



Destruction of the old bottom fauna . . . ; 327 



Terminology with reference to degree of pollution and tolerance 333 



Hydrographical subdivision 334 



Summary 336 



Upper Peoria Lake and the Illinois River, Chillicothe to Spring Bay 

 (Mile 146.5—153.2 below Lake Michigan): 



Hydrography 338 



Dissolved oxygen 339 



Small bottom animals 341 



Middle Peoria Lake, Mossville to Al Fresco Park (Mile 154.9 — 159.3 

 below Lake Michigan): 



Hydrography 353 



Dissolved oxygen '. 354 



Small bottom animals 356 



Lower Peoria Lake and Illinois River, Peoria Narrows to Peoria and 

 Pekin Union Railway Bridge (Mile 161.0 — 166.4 below Lake 

 Michigan) : 



Hydrography 365 



Dissolved oxygen 366 



Small bottom animals 367 



Comparison of the recent small invertebrate bottom and weed fauna of 



Peoria Lake with that of 1913-1915 377 



Commoner small bottom animals that have disappeared since 1915 379 



Almost complete extinction of an abundant and varied mussel fauna 



since 1913-1915 384 



Bibliography 387 



Comparison of 1922 and 1920 species lists, detail 389 



