survey but the pup8« occurred in stone-covered silk cocoons with the under- 

 side bare of stones, and. the anterior end open so that the respiratory 

 organs protrude. The larvae feed mainly on algae. They were most commonly 

 found from mile 285.9 to mile 229.8. 



Simulidae . The black flies are phytophagovts in their larval 

 stages. The larvae have a fan of hairs around the mouth with which to 

 brush bits and pieces of plant material toward the mouth. Near the ante- 

 rior end are prolegs which enable the animal to move about. At the pos- 

 terior portion of the abdomen is a sucker-like disc surrounded by rows 

 of hooks. The function of this disc Is to assist the euaimal to retain 

 its position on a rock in rapid water. The pupa is partially ensheathed 

 in a cocoon and normally the respiratory orgauis extend out of the pupal 

 ceise. Some species of this family have been characterized as pollution 

 indicators, but most of this group is found in rapidly flowing waters with 

 high dissolved oxygen content. In some trout streams, animals may be 

 svifficiently numerous to make rock surfaces slippery and hazardous to 

 anglers . 



Tendipedidae . The midges axe one of the most diverse groups 

 in the order Diptera. Fowc of the six subfamilies were collected from 

 the Sacramento River. Only Podonominae, restricted to high mountain 

 country, and Clunionlnae, which is almost exclusively a marine, were not 

 seen. The larvae of these animals occupy a wide range of terrestrial 

 ajid aquatic habitats. Certain species tend to be confined to particular 

 environments. Greater knowledge of life histories and physical and chemi- 

 c8lL requirements, menibers of this group may be useful as pollution indicators. 



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