SWIFT STREAMS 



97 



year to year. On one occasion the surface of the rocks and stones in 

 Thorn Creek was almost covered with sponge, and while some sponge is 

 always to be found, we have not seen it so abundant again. Polyzoa 



Representative Fishes of a Rapids Community 

 Fig. 44. — The banded darter {Etheostoma zonale); length 2 in. (from Forbes). 

 Fig. 45. — The rainbow darter (Etheostoma coeruleum); length 2 in. (from Forbes). 

 Fig. 46. — Black-sided darter (Hadropterns aspro); length 3-4 in. (from Forbes). 



are usually present under the stones. Such animals depend upon foods 

 in solution and small floating plants and animals. 



In addition to those rapids which have large rocks, are those in which 

 the bottom is of coarse sand and gravel, with only a few small stones. 



