50 University of California Publications in Zoology [Vol.22 



Amphiprora (data Kiitz. 



Station I Station II Station III Daily Hourly 



Average 12,847 4,161 21,057 8,373 268,548 



Identification satisfactory as to genus and probable as to species. 

 A. ornata is probably included in the count at times, as it was some- 

 times found by the writer and was also identified in 1915 catches by 

 Professor C. J. Elmore. Probably heavy loss through the net. So far 

 as net catches show it is not so very important. Occurrence rather 

 scattering at all stations though fairly constant in latter part of the 

 year at Station I. Maximum at Station I in May, at other stations in 

 June. 



Bacillaria paradoxa Gmel. 



Station I Station II Station III Daily Hourly 



Average 8,547 1,647,817 984,810 28,857 254,916 



Identification positive. Colonies usually large, hence probably 

 very little loss through the net. Occurrence scattering at Station I, 

 fairly constant through the year at Station II and III where it was 

 abundant through the second half year. Maximum in July at Station 

 I, August 2 at Station II, and August 9 at Station III. Conspicuous 

 minor pulses in April and December at Station II ; April, September 

 and December at Station III. The sudden jump into prominence at 

 Stations II and III in July and the reappearance at Station I, where 

 it had been absent more than two months, seems to indicate favorable 

 influence of stagnant water. Retardation by sewage is also indicated. 

 Higher temperatures may have a bearing, though the temperature 

 change is not nearly so abrupt as the change in numbers of Bacillaria. 

 There are no very strong indications of recurrent pulses at any station, 

 but Station II shows them slightly. 



B. paradoxa is certainly one of the most important planktonts of 

 the river after the flood season. Colonies containing less than ten indi- 

 vidual cells were comparatively rare, certainly not more common than 

 those consisting of more than twenty-five. It would be very safe to 

 estimate the average number of cells captured at ten times the aver- 

 age recorded for the colonies. This would bring B. paradoxa into the 

 foremost rank of planktonts, numerically, at Stations II and III. Only 

 Cyclotclla sp. and Mclosira granulata would clearly exceed it in num- 

 bers by that reckoning. The other forms which might do so are not 

 identified with sufficient certainty. 



Cocconcis pcddculus Ehrbg. 



Determination probable. May include other species. Losses through 

 net undoubtedly heavy. According to the records not a very import- 



