Fig-. 122. One of the hot sulphur springs along the Yellowstone River. This 

 particular spring lies at the base of a hollowed rock shown in upper 

 middle of figure 119. 



Fig. 123. May-fly nymphs from the Lamar River ; four times actual size. 

 Middle specimen turned over to show the " sucker " on under side, by 

 means of which this particular species clings to rocks. 



