415 



• 



2. Leeches (Hirudinea). 



At least four or five species, including ai)parently, Erfyobdclla punc- 

 tata (Leidy). and two species of Melobdella : taken in all zones of the 

 river and lake, from Lacon southward, 1!l"^;!. The sjjccies of Er]i()hdel]a 

 mentioned was definitely associated with ijollution in W'eston and Turner's 

 studies of the Coweeset River in 1!»11. 



3. Midge Larvae of pollutional habit. (Chironomidae) 



Chironomus pUimosus Linnaeus, var. 



Chironotnus decants Johannsen 



Cliiroiioimis lobifcnis Say 



Several undetermined Cliironominac and Tanypinae, like the 



three species of Chironomus preceding, with range from Chilli- 



cothe or head of upper Peoria Lake, south. 



4. Other Chironomidae, witli distribution for most part from middle or 



lower Peoria Lake southward. 



Chirononiiis digitatus Malloch 



Cricotopus species 



Orthocladius 



Palpoiiiyia spp., probably two. 



Forcipoinyia species 



Procladiits species 



Tally pus species 



Unidentified Chironominae and Tanypinae, several species. 

 It is quite possible that some of these imperfectly determined forms 

 are in reality species with distinct preference for clean bottom ; but occur- 

 rence in Peoria Lake, even in the outer zones, in its recent condition, may 

 be taken to indicate rather more than the degree of tolerance shown by the 

 more sensitive species of that description. 



5. Sphaeriid Snail of especially tolerant habit. 



MitscuUum transvasum Say. This species was found associated 

 with sludge worms of the genera Limnodrilus and Tubifex, where there 

 was almost complete oxvgen exlmustion one foot from bottom, both in 

 1020 and 1922. 



6. Sphaeriid Snails of less tolerant* habit. 



MuscuUum truncatmn Linsley 



Pisidium coniprcssum Prime 



Pisidiuiii coin planat urn Sterki 



Pisidium paupcrculum var. ciystalcnse Sterki 



Pisidium species 



Sphacrium staiiiinciim Conrad 



Sphacrium striatiuum Lamarck 



Sphacrium striatiuum var. lilycashcnsc Baker 



Sphacrium species 



• The distribution of this subdivision of group I. ami reasons for their distinc- 

 tion in degree of tolerance from other Illinois River snails. Is discussed In detail 

 In the 1922 paper on Peoria Lake. 



