9 8 



ANIMAL COMMUNITIES OF STREAMS 



53 



54 



REPRESENTATIVE ANIMALS or A RAPIDS COMMUNITY 



FIG. 47. An adult brook beetle (Parnidae); twice natural size (original). 



FIGS. 48-50. Different views of the nymph and adult of the May-fly (Siphlurus 

 alternatus); 3! times natural size (after Needham). 



FIG. 51. The eggs of a tabanid fly taken from a protruding stone; twice 

 natural size (original). FIG. 52. Adult fly. 



FIG. 53. A water-strider (Rhagovelia collaris), from the margin of the swift 

 brook (New Lenox, Gaugars) ; twice natural size. 



FIG. 54. The common river snail (Goniobasis livescens), covered with calcium 

 carbonate secreted by algae; natural size (original). 



FIG. 55. An intermittent stream sowbug (Asellus communis); twice natural 

 size (original). 



