46 University of California Publications in Zoology [Vol.22 



Selenastrum bibrainum Keinsch. 



Identification satisfactory. Recorded five times from Station I in 

 small numbers. Once at Station III. Evidently too small to be held 

 by the net. 



The following forms were recorded only once or twice in small 

 numbers or else were noticed in living material. 



Botryoeoccus sp. Once at Stations II and III. May have been overlooked. 



Bulbochaete sp. 



Chodatella eiliata. Lemm. Once at Station III. 



Crueigenia quadrata Morr. Once in daily series. 



Crucigenia reetangularis Chod. 



Crueigenia sp. Once at Stations II and III. 



Dimorphococcus lunatus A. Br. 



Draparnaldia plumosa Ag. 



Golenkinia radiata Chod. Once at Stations I and III. 



Lagerheimia wratislaviense Schroed. Once at Station I. 



Lauterborniella elegantissima Schmidle. Once at Stations I and II. 



Monostroma sp. Once at Station III. 



Nephrocytium agardhianum Naeg. 



Pleurococcus sp. 



Sorastrum spimilosum Naeg. 



Stigeoclonium (?) sp. Twice at Stations I and II. 



Tetrastrum sp. Once at Station III. 



Ulothrix sp. Twice at Station I. Doubtful identification. 



Bacillariaceae 



Plates 7-9 



Station I Station II Station III Daily Hourly 



Number of forms recorded 44 58 53 25 32 



Av. number per cu. meter 22,609,062 39,478,317 36,826,859 28,055,459 29,029,248 



The diatoms are distinctly the most abundant group of organisms 

 in San Joaquin plankton so far as present methods show. According 

 to these records they outnumber Sehizophyceae 14, 33 and 18 to 1 ; 

 Chlorophyceae 12, 28 and 21 to 1, and Mastigophora 6, 14 and 7 to 1 

 at Stations I, II and III respectively, thus making them appear to 

 have a still more prominent place in the plankton than they had in 

 Illinois. There were always some diatoms in every collection at all 

 stations throughout the year. 



There was only one very distinct pulse at each station. At Station 

 I this appeared in May, while at the other stations, where it was larger 

 but less abrupt, it came in August. There is no way of telling from 

 these records whether this difference was due to better temperature or 

 to more stable conditions at those times. The fact that Smith Canal 



