1920] Allen: Plankton of the San Joaquin River 35 



organisms, but also that it probably holds a high place in working up 

 the organic content of the water. Identification, even of genera, was 

 frequently rather difficult in this group, although there was not often 

 any question as to their belonging to the Schizophyceae. Names as 

 recorded are to be regarded as suggestive rather than positive. 

 Eyferth's Einfachste Lcbensformcn and Tilden's Minnesota Algae 

 were the guides mainly used. 



Discussion of Species 

 Anabaena spp. „ T „ „ ., „ , 



rl Station I Station II Station III Daily Hourly 



Average 57,600 317,644 437,967 245,139 1,531,949 



Not clearly distinguished from Nostoc, straight filaments being the 

 characteristic usually considered indicative. Includes some Aphani- 

 zomenon. Pound occasionally throughout the year. Abundant only 

 in July, August and September, at all stations, in a water tempera- 

 ture ranging from 23.5° C. to 28° C. Largest number recorded at 

 Station I on July 12, Station II on August 9, and Station III on 

 July 19. 



Aplianocapsa spp. 



Station I Station II Station III Daily Hourly 



Average 117,381 84,916 74,329 441,469 187,647 



Most of the colonies counted under this name probably belong un- 

 der Clathrocystis and Microcystis. There were probably few, if any 

 Aplianocapsa present. The characteristics of Aplianocapsa were not 

 understood until the count had gone too far for revision. Since 

 Clathrocystis and Microcystis were also more or less subject to con- 

 fusion it was thought best to let the record for 1913 stand under this 

 head. The maximum production occurs at about the same time as 

 that of Microcystis at all stations. Hence the error probably affects 

 nothing but the question of species distribution. Clathrocystis does 

 not appear on the record though now known to be present and it 

 might be well to transfer the Aplianocapsa count to that heading. 

 The late summer maximum, occurring in higher temperatures and 

 the sudden fall in numbers in colder waters suggests the character- 

 istics of Clathrocystis as noted by Kofoid (1908) in Illinois. 



Coelosphaerium kiitzingianum Naeg. Recorded three times from 

 Station III and once from each of the other stations. Very small 

 numbers in all cases. Identification not positive. 



