1920] Allen: Plankton of the San Joaquin River 63 



Discussion of Species 

 Clostermm acerosuni Elirbg. 



station I Station II Station III Daily Hourly 



Average 539 7,108 6,161 206 10,961 



Identification uncertain. Losses through net probably large. Oc- 

 currence rare, irregular and in small numbers at Station I. Found 

 at almost all times of year at other stations. Maximum in September 

 at both. Evidently favored by higher temperatures. 



Closterium acumitiatum. 



Identification doubtful. Recorded three times at Station II and 

 five times at Station III. 



Closterium rostratiim Ehrbg. 



Station I Station II Station III Daily Hourly 



Average 21,580 8,322 4,494 929 3,045 



Identification satisfactory. Losses through net probably large. 



Recorded only seven times at Station II, five times at Station III and 



occurrence rare at Station I until late summer. Maximum at Station 



I in August. Distinctly a summer planktont. Apparently favored 



by sewage. 



Mougeotia sp. 



station I Station II Station III Daily Hourly 



Average 7.5,517 262,429 269,657 23,118 793,870 



Identification of genus satisfactory. This was decidedly the most 

 abundant of the filamentous Conjugate. Rather prominent at all sta- 

 tions in July, August and September with maximum in last week of 

 August or first of September. Not found often or in large numbers at 

 other times. Favored by temperatures above 20° C. and somewhat 

 hindered in development by sewage. 



Spirogyra protecta Wood. 



Identification uncertain. Occurred once at Station I, five times 

 at Station II and nine times at Station III. Never in very large 

 numbers. So far as catches show it is unimportant in every way. 



Staurastrum sp. A. 



Station I station II Station III Daily Hourly 



Average 8,741 97,529 128,529 1,548 87,419 



Genus certain. Species description not found in any literature 



available. Only the more voluminous references at the University of 



