381 



also in the summer of 1932 within less than a hundred feet of the bank 

 at the lower end of the upper lake, but the other appeared in none of 

 our collections from anywhere between Chillicothe and Peoria in 1930 

 and 1922. These two species, while evidently partial to shallow weedy 

 waters, also habitually spread far from shore in our local bottomland 

 lakes; occurring in lakes near Havana in 1914 and 1915 in six to 

 nine feet of water on plain mud bottom, and in the four to seven foot 

 depth zone in upper Peoria Lake before 1930. A species of Ainnicola 

 near A. liiiwsa Say, partaking of the habit of the Vaivatas just de- 

 scribed, of becoming bottom or weed species at will, was taken in the 

 shallower areas of the upper and middle lakes before 1920. 



Other bottom-dwelling snails taken in Peoria Lake in 1913 and 

 191.") collections but since then not seen, included one or"more species 

 of the little lini]X't-like .'Xncylus, which was formerly common on shells 

 and sticks in the deeper water near the channel; a species of Pleuro- 

 cera, P. sitbularc Lea, which occurred less commonly than its more 

 abundant congener, P. clcvatum lennsii, which latter species still per- 

 sists in small numbers in the more rapid current in the lower lake ; 

 and the comparatively large amnicolid Somatogyriis siibglobosus Say, 

 which was taken in small numbers only in the upper lake. 



INSECTS 



Among larvae and nymphs of insects which have recently disap- 

 peared entirely from open-water dredgings in all three lakes the most 

 important are members of the family Ephemeridae, or May-flics; of 

 several families of Odonata, or dragon-flies ; and of the commonest 

 of the midge families locally, the Chironomidae. 



In 1913 and 1915 the common May-fly, Hexagenia variabilis 

 Eaton, was occasional in collections from both the middle and lower 

 lakes, but has not since been taken in the Illinois River above Havana. 

 Specimens of two other genera of May-flics that have since failed to 

 appear, Callibaetis and Caenis, were also taken several times in the 

 course of the dredging before 1980 in the two lower lakes. 



The principal Chironomidae that have disajipearQd include Ciii- 

 ronomus tentans Fabricius, formerly one of the most generally dis- 

 tributed and abundant, and because of its large size most conspicuous 

 of the midge larvae of Peoria Lake and other middle Illinois River 

 situations during the summer season. Other larval midges definitely 

 missing recently, include Chironomus nigricans Johannscn ; one or more 



