108 ILLINOIS BIOLOGICAL MONOGRAPHS [206 



EXPLANATION OF PLATE 



Fig. 12. Salt Fork three and a half miles above Homer Park, Station 23. October 4, 

 1918. 



FiG. 13. Salt Fork. Deep pool below dam and rapids. Professor Smith's field laboratory 

 during a period of twenty years. Station 25. November 4, 1920. 



