54 University of California Publications in Zoology [Vol. 22 



Gyrosigma acuminatum Kiitz. 



Station I Station II Station III Daily Hourly 



Average 1,232 24,920 22,157 _ 12,207 



Identification uncertain. Recorded seven times at Station I at wide 

 intervals, twelve times at Station II and Station III. Grouped in 

 August at Station III. Considering amount of loss through net may- 

 have some importance though evidently adventitious. 



Gyrosigma kiitzingii Griin. 



Station I Station II Station III Daily Hourly 



Average 3,330 102,723 70,433 1,032 87,974 



Identification probable. Losses through net very heavy. Recorded 

 frequently in small numbers in every month except February, June, 

 and July at Station I. Maximum there in September. Occurred regu- 

 larly with only one or two breaks at Stations II and III. Maximum 

 at Station II in late August in a well developed pulse. Maximum at 

 Station III in late July at the beginning of a similar pulse which 

 almost reached the maximum again at the same time with Station II. 

 Minor pulses at from two to six weeks intervals through most of the 

 year were rather prominent at both stations. Apparently this is a 

 planktont of some importance throughout the year since the percent- 

 age retained by the net is undoubtedly small. 



Gryrosigma scalproides Rabenh. 



Station I Station II Station III Daily Hourly 



Average 13,733 31,294 206,444 826 480,133 



Identification satisfactory. May include G. spenceri W. Sm. Loss 

 through net heavy. Records scattering at Station I especially in first 

 seven months. Maximum in August with a well developed pulse. 

 Recorded in every month up to September and not later, at Station II, 

 with a sharp pulse in August. Recorded every month after January 

 and February at Station III though scattering until late July. Very 

 strong pulse in August reaching apex on August 23. Seems to be, 

 like other Gyrosigma, a seasonal planktont favored by temperatures 

 above 20° C. and injured by sewage. 



Melosira granulata Ehrbg. 



Station I Station II Station III Daily Hourly 



Average 2,305,175 25,163,409 22,821,226 1,880,779 18,144,471 



Identification certain. Mostly variety spinosa. Loss through net 

 high. Kofoid (1908) says about 98 per cent in Illinois and it is doubt- 



