58 University of California Publications in Zoology [Vol.22 



Navicula sp. 



Under this head are included a number of forms thought to be 

 Navicula. Some of these were first recorded as N. oblanga, N. pusilla, 

 N. rhombaides and N. smithii, but the numbers were few and the iden- 

 tity uncertain, so it was more convenient to place them this way. 

 There is nothing of particular importance to be obtained even from 

 the combined record. 



Navicula viridis Ehrbg. 



Station I Station II Station III Daily Hourly 



Average 169 27,659 4,488 985 



Identification satisfactory. Losses through net probably heavy. 

 Numbers very small at Stations I and III. Maximum in May at 

 Station II where the numbers were larger and there were few col- 

 lections showing none. For purposes of discussion it is unfortunate 

 that the only Navicula named with confidence presents too few num- 

 bers to warrant much attention. 



Nitzschia acicularis Kiitz. 



Station I Station II Station III Daily Hourly 



Average 2,878,662 316,042 476,223 4,390,368 600,166 



Identification satisfactory. Probably very small percentage re- 

 tained by net. Present throughout the year at all stations. Maxima 

 in June at Stations I and II, in late August at Station III. Numbers 

 well sustained through summer at all stations, with a conspicuous 

 September pulse. Evidently a summer planktont favored by tem- 

 peratures above 20° C. Just as evidently favored by the sewage at 

 Station I as shown by the enormous averages there in comparison with 

 the averages at other stations. Recurrent pulses fairly well marked. 

 Certainly of great numerical importance though its small size would 

 keep the volumetric showing low. 



Nitzschia spp. 



Under this heading are discussed four or more species of Nitzschia 

 all but one of which are doubtful as to identification. Nitzschia angu- 

 laris was satisfactorily determined but N. sigma, sigmoiclea and vermi- 

 cularis were all somewhat doubtful, at least sometimes. They were 

 all listed separately in the tables but the occurrence was so erratic and 

 the probable losses from the net so heavy that it hardly seemed worth 

 while to attempt to draw any conclusions from the records of any of 

 them. It might be noted, however, that all Nitzschia are favored by 

 higher temperatures, but that none of these do well in sewage, N. 



