Vll 



PAGE 



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 extermination of an abundant and varied mussel 



fauna since 1913-1915 384 



Bibliography 387 



Comparison of 1922 and 1920 species lists, detail 389 



ARTICLE VI. ILLINOIS RIVER BOTTOM FAUNA IN 1923. BY 



ROBERT E. RICHARDSON. October, 1925 391-422 



Introduction 391 



Summary 392 



Illinois River above Peoria Lake, La Salle — Chillicothe, 44 miles.... 393 



Peoria Lake, Chillicothe— P. P. U. Bridge, 20 miles 394 



Illinois River below Peoria, P. P. U. Bridge — Beardstown, 71.5 miles 405 



The missing small bottom animals of the 1913-1915 species lists, ap- 

 parently exterminated some time between 1915 and 1920. Head 



of Peoria Lake to Beardstown 410 



Small bottom invertebrates of Illinois River and Peoria Lake, La- 



Salle to Beardstown, 1923 414 



Pre-1920 bottom species recently missing from Illinois River and 

 Peoria Lake dredge hauls 418 



ARTICLE VII. SOME OBSERVATIONS ON THE OXYGEN RE- 

 QUIREMENTS OF FISHES IN THE ILLINOIS RIVER. BY 



DAVID H. THOMPSON. October, 1925 423-437 



Introduction 423 



The general relation of ice and dissolved oxygen 423 



Recent observations on the relation of ice and dissolved oxygen in 



the Illinois River 424 



The effect of low dissolved oxygen concentrations on the fishes of 



the Illinois River 429 



The effect of dissolved oxygen concentration on the fish yield of the 

 Illinois River 435 



ARTICLE VIII. AN ENTOMOLOGICAL SURVEY OF THE SALT 

 FORK OF THE VERMILION RIVER IN 1921, WITH A BIBLI- 

 OGRAPHY OF AQUATIC INSECTS. BY CHARLES P. ALEXAN- 

 DER. OcToBwt, 1924 439-535 



Introduction iH 



The Salt Fork from a biological view-point 439 



Sewage entomology 440 



Description of the stations made in the 1921 survey of the Salt Fork 442 



Water conditions by stations briefly summarized 443 



Record of collections made at the various stations 443 



