1920] Allot: Plankton of the San Joaquin River 79 



Raphidiophrys elegans H. & L. 



Station I Station II Station III Daily Hourly 



Average 309,635 79,467 107,739 532,371 20,345 



Identification probable. First recorded in April at Station I and 

 Station III, in March at Station II. Constant in occurrence at 

 Station I through June, July, August and November. Irregular at 

 other times. Irregular at both the other stations except for a period 

 through August and early September at Station II, late June and 

 July at Station III. Evidently favored by higher temperatures and 

 sewage, not so much by stagnation. From these records, seems to be a 

 rather important constituent of our plankton. This is somewhat dif- 

 ferent from the condition at Illinois where it appeared only as a con- 

 stituent of back waters. 



The following forms were recorded only once or twice or were 

 thought to be present in living material. 



Aetinosphaerium eichornii Ehrbg. Once, I and III. 

 Diploeystis sp. 

 Vampyrella sp. Once, III. 



Ciliata 



Station I Station II Station III Daily Hourly 



Number of forms recorded 32 22 25 9 10 

 Number of individuals 



per cubic meter 946,762 447,909 431,445 1,306,075 3,136,5S3 



Identification of ciliates was about as unsatisfactory as was that 

 of the Rhizopoda and Heliozoa. This was due partly to distortion of 

 preserved specimens and partly to small size. It is probable, how- 

 ever, that totals for the group are fairly accurate. 



Members of the group were always found throughout the year, 

 except for the first three and two collections at the first of the year 

 at Stations II and III respectively. Unfortunately no general con- 

 clusions can be stated with full confidence from the totals of Protozoa 

 because Vorticella sp. is too largely responsible for them. This was 

 because Vorticella sp. was used as a sort of catchall for a miscellaneous 

 assemblage of organisms which could not be readily distinguished 

 under conditions of counting. Most of these were. clearly Vorticella 

 (nearly all of the short stem type) but some craspemonad flagellates 

 and the like were undoubtedly counted in at times. In spite of these 

 defects in the record, there is some reason for thinking that the group 

 as a whole develops best in sewage water and in the higher tempera- 

 tures with rather stable conditions. Since this does not agree very 



