56 University of California Publications in Zoology [ VoL - 22 



No effort was made to determine the average number of cells in a 

 filament but it was probably not less than five. The cells composing a 

 filament were much longer in proportion to width than they were fig- 

 ured in the literature consulted. A common form about the time of 

 maximum numbers had cells about five times as long as wide. 



Melosira varians Ag. 



Station I Station II Station III Daily Hourly 



Average 4,682 233,227 93,884 619 9,123 



Identification satisfactory. Losses through net heavy. Occurrence 

 at Station I quite irregular in small numbers, with a maximum in 

 April. Main production at other stations in first six months, two or 

 three misses after that time at both. Maximum at last of May in Sta- 

 tion II after steady increase for several weeks. Maximum in March 

 at Station III, appearing rather abruptly. Recurrent pulses at two 

 to six weeks intervals at both stations. A large September pulse is 

 only indication of response to conditions similar to those of M. granu- 

 lata. In fact the most favorable temperature seems to be near 18° C. 

 or between 12° C. and 20° C. There is a strong pulse in late Decem- 

 ber at Station II which follows about a month of temperatures below 

 10° C. Hence it is certain that the two species are distinctly different 

 in the responses to temperature. "While M. varians is overshadowed in 

 productiveness by M . granulata, it is yet to be reckoned an important 

 planktont here. 



Navicula affinis Ehrbg. 



Identification doubtful. Losses through net heavy. Recorded 

 eleven and eight times at Stations II and 111 respectively in rather 

 small numbers. Not sufficient data for discussion. 



Navicula alpestris Grun. 



Station I Station II Station III Daily Hourly 



Average 6,746 76,645 29,979 3,929 55,357 



Identification doubtful. Losses through net very heavy. Occur- 

 rence at Station I in small numbers and very scattering through the 

 year. Not much better record at Station III. Appears in March at 

 Stations II and III. Maximum at Station II on May 31 after two 

 months of fairly steady increase, followed by slow decline to August. 

 Seems to be favored by moving water. Its long continued presence 

 seems to indicate that it is a true planktont, and it is probably of 

 considerable importance. 



