414 



Total Numbers of Group II, or CLEAXiai-PREFEEENCE Species. 



Compared avitii Total Number of Collections. 



1920-1923 



• Purpose of this table to show that adding in the 1920 and 1921 collections 

 adds very little — except in the Matanzas-Beardstown section — to the total number 

 of Group II species taken in 1923. 



t The upper line of fleures aeainst an entry Kives the number of species; the 

 lower one. the number of collections. 



t A dash indicates no collection. 



Small Bottom Invertebrates* of Illinois River and 

 Peoria Lake, La Salle to Beardstown, 1923 



Group I 



POLLUTION,\L OR MORE OR LESS TOLERANT SPECIES t 



1. Small Annelid Worms. (Tubificidae) 



LimnodrUus species like L. Iioffiiicistcri Claparede 

 Limnodrilus species like L. daparcdcianus Ratzel 

 LimnodrUus species 

 Tiibifcx tithifcx Miiller, or var. 

 Titbifcx species, apparently undescribed. 

 Dcro species, one occurrence, outer zone, Peoria Narrows. 

 Other Oligochaeta, unidentiticd, in bad state of preservation, or 

 immature, several thousand specimens. 



♦ No mussels included except very younp individuaLs or dwarf species, taken 

 with 1/12 sq. yd. Petersen sampler. 



t See definitions of terms in introduction. 



