• 406 



bottom animals, practically all of common occurrence at some stations in 

 the range, which have since then disapiieared from collections altogether; 

 pp. 413 and 419. Here, in the first eight miles aljove the Spoon River 

 bar, at Havana, sedimentation is especially active at times of floQd reces- 

 sion, finally depositing on the bottom a gOodly portion of the load of more 

 or less putrescible svispended solids that mostly passed over the heads of 

 the bottom animals in the reaches between Liverpool and Peoria. Below 

 Havana, in the thirty odd miles to Beardstown, in the summer of 1023 only 

 six group n species were found in a total of thirteen bottom hauls taken. 

 This section of the Illinois, was, however, rather noticeably ]Kior in bot- 

 tom species at most of the stations worked in the seasons of collecting be- 

 tween 1913 and 1915 ; though even our lists from it show a total of fully 

 two dozen kinds of small bottom animals that have failed altogether to 

 appear in collections made since and including 19"30. 



Decrf.\sk of Both Grovp I and Groii' II* Spbcies 

 FKOM Pkori.v Lake Southward, 1923 



* Ch'aner preference group. 

 t Mnsculium ti'ansrersum. 



