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 
46 
REPRESENTATIVE FISHES OF A RAPIDS COMMUNITY 
Frc. 44.—The banded darter (Etheostoma zonale); length 2 in. (from Forbes). 
Fic. 45.—The rainbow darter (Etheostoma coeruleum); length 2 in. (from Forbes). 
Fic. 46.—Black-sided darter (Hadropterus 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. 
