1920] Allen: Plankton of the San Joaquin River 69 



Cryptomonas sp. 



Identification doubtful. May be confused with some other forms. 

 Loss through net heavy. Recorded at Station I in considerable num- 

 bers in latter part of year. Only once at Station II and four times 

 at Station III. Distinctly favored by sewage and low temperature 

 but relatively indifferent to quiet water by this showing, which agrees 

 pretty well with Kofoid's findings (1908) in Illinois. 



DinohryoH sertularia Ehrbg. 



station I Station II Station III Daily Hourly 

 Average 11,481 9,993 [.. 



Identification of species frequently uncertain. Loss through net 

 probably large. Occurrence rare at Station I and in small numbers 

 of colonies at that. Recorded eleven times at Station II in four, well 

 marked groups at the last of March and May, first half of June and 

 through most of November. Maximum in May and June. Recorded 

 frequently at Station III from March to July and again in November. 

 Absent at other times. Favored by cooler water or flood time and 

 hindered by sewage. Although the numbers here were small the 

 distribution resembles that recorded for Illinois most remarkably. On 

 the present showing it cannot be regarded as a very important plank- 

 tont here. While not followed very far, the general impression given 

 by the condition of the colonies here leads to support of Kofoid's 

 contention (1908) that the synonymy of this species has been need- 

 lessly extended and that all the variant forms might be included 

 under one species name with advantage. 



Eudorina elegans Ehrbg. 



station I Station II Station III Dailv Hourly 



Average 11,277 84,27.5 71,776 9,351 376,375 



Identification usually certain. Found throughout the year at 

 Stations II and III with only six scattered periods of absence at each. 

 Numbers much smaller and absences more apparent at Station I 

 where it M^as only twice recorded in May, entirely absent in August 

 and most of September, last half of October and first half of Novem- 

 ber. Evidently deleted by sewage. Maximum in October at this 

 station, on August 9 at Station II and III. Contrary to the Illinois 

 record the period of greatest abundance in our river is in the warm- 

 est season and almost at greatest stagnation. The complete absence 

 at Station I at this time, however, may throw some light on the Illinois 

 situation. Either the sewage is more injurious to this organism in 



