usually long with extremely fine claws wMch axe in most instances re- 

 tracted so as to be discerned only with careful examination. 



EcologicsLLly, this species seems to he one of four of the 

 Tendipedidae which has heen able to adapt to life in the grinding, shift- 

 ing sands of the river bed load, and this one is found most regularly. 

 The others are members of the following genera: Pentapedilum , Polypedilum , 

 and Cricotopus . Most members of the genus Cryptochironomus are found 

 in slower moving waters, and some are miners in the stems and leaves of 

 aq.uatic plants. 



Larvae and pupae of Pentapedilum and Polypedilum were found 

 most regiolarly in the upper-middle reach and occasionally in the lower- 

 middle reach. 



MoLLvisca 



Pelecypoda . The asiatic clam Corbicula fluminea, has become 

 a serious pest in certain California rivers and canal systems. There 

 did not appear to be any thick beds of these clams in the Sacramento River 

 such as occxir in some other streams and ceuials. Corbicula does, however, 

 appear to be able to maintain a significant population under severe condi- 

 tions of a moving bed load and was found as far upstream as mile 90*5 and 

 in Colusa Basin Drain (mile 90. 2R). Far greater niimbers of small indi- 

 vidxials were found than full grown clams. It is possible that as yet 

 xindiscovered concentrations of these individuals exist in the river, or 

 the population is just beginning to bloom. At any rate, it will be inqpor- 

 tant to follow the development of this population of small clams. 



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