408 



Total Tiiukicidak am) T. iiniiKX Takkx Below PEoitfA. 1923* 



AVT.RAGE NOS. I'KK S(J. Yl). 



Total Tubificidae 



Outer 

 zone 



940 



1,458 



2.196 



48 

 4,392 



640 

 7,056 



12 



48 



12 



36 



Wesley 



7 mi. Island 



2 mi. above Pekin in 

 dredge ditch 



Pekin 



Old mouth Mackinaw 



Mackinaw 



Kingston Ferry 



Lancaster 



Cop. Cr. abv. Dam 



Cop. Cr. below Dam 



Spring L. Canal inside 

 mouth 



Liverpool 



Quiver Beach 



Havana 



Matanzas 



Foot Grand Isl. 



Hd. Hickory Isl. 



Mouth Sangamon 



Beardstown 



• To show decrease down .stream frmn Peoria. Compare with virecediiiK table. 



Tubifex tubifex 



Inter- 

 Channel mediate 

 zone I 



Outer 

 zone 



12 



48 



When we compare with the hottoin collections made in l!V20-^the 

 last preceding^ date when we made hauls in the Illinois River helow Peoria 

 Lake — it is found that there were in all twenty group II or cleancr- 

 ])reference species taken in li)2;) in forty-nine collections in the seventy 

 odd miles of river between Wesley and Beardstown, to only thirteen 

 in thirty-six collections in a somewhat reduced distance within the same 

 section in the summer three years preceding. Sharp increase over 1920 



