74 University of California Publications in Zoology [Vol. 22 



Trachelomonas euchlora Lemm. 



Station I Station II Station III Daily Hourly 



Average 14,295 21,739 30,180 7,032 56,965 



Identification uncertain. Small percentage retained by net. Pound 

 frequently in first half year at all stations. Rare in second half year. 

 "Warmer waters, sewage and stagnation seem to be deterrent, since 

 numbers were smallest at Station I and during the period from June 

 to October. 



Trachelomonas volgensis Lemm. 



Identification probable. Loss through net very heavy. Recorded 

 five times near last of year at Station II and six times at Station III. 



Trachelomonas volvocina Ehrbg. 



Station I Station II Station III Daily Hourly 



Average 268,091 134,297 180,692 179,473 512,684 



Identification uncertain. Loss through net very heavy. Recorded 

 in every month at all stations. Maximum at Station I on August 20, 

 at Station II on September 13, and at Station III on August 31. 

 "While a number of minor pulses are readily distinguishable at all 

 stations, the percentage of loss is too uncertain to encourage conclu- 

 sions. The maxima of the three stations coming so close together lead 

 to the idea that temperature is an important factor for this form 

 and that it does best above 20° C. The difference in averages listed 

 above supports the view that sewage is beneficial and this is strength- 

 ened by the fact that several catches at Station I exceed the maxima 

 at Station II and III. Stagnation seems favorable at all stations. 



Volvox aureus Ehrbg. 



Identification satisfactory. Recorded only at Station II, five 

 times in August and September. 



Volvox globator L. 



Identification satisfactory. Recorded only at Station III twice, in 

 September and December. 



The following forms of Mastigophora were recorded only once or 

 twice, or else they were thought to be present in fresh material : 



Anthophysa sp. Once, I and Daily. 



Chilomonas paramoecium Ehrbg. 



Dinema sp. Once, III. 



Diplosiga sp. All stations. Not counted because too small. 



Diplosigopsis entzi France. Once, II. 



Euglena aeutissima Lemm. 



Gonium pectorale O. F. M. Once, II and III and Hourly. 



