278 A NATURALIST IN THE GREAT LAKES REGION 



substratum, others burrow only in sand, and still others require 

 the soft mud in which to lie concealed. 



It is evident, then, that streams present a great variety of 

 habitats and, therefore, a number of animal and plant societies, 

 which may be tabulated somewhat as follows : 



A. Communities of the intermittent stream 



1. Intermittent rapids society or the Simulium (black 

 fly) association 



2. Intermittent pool society or the Cambarus diogenes 

 association 



3. Permanent pool society or the horned dace association 



B. Communities of permanent streams 



4. The spring-fed brook or planarian association 

 a) Of the usual alkaline stream 



5. The very rapid water (lotic) society or the Hydro- 

 psyche association 



This is a rock-bottom society and may be subdivided 

 into 



a) Rapids of the brook, Johnny darter association 



b) Rapids of the creek, fan-tail darter association 



c) Rapids of the river, banded darter association 



6. The moderately rapid, sand-bottom society 



a) Of the brook 



b) Of the creek 



c) Of the river 



(both divisible 



7. The sluggish water surf ace association I as the forego- 



8. The sluggish water bottom association ling into a), b), 



(c) 



9. The estuary associations 

 10. The acid stream society 



It would require a volume rather than a chapter to discuss in 

 detail the stream societies and subsocieties with anything like 



