1920] Allen: Plankton of the San Joaquin River 29 



Major Groups of Plankton 



ALGAE 



No plants higher than the algae have been found in these collec- 

 tions. Very few baeteriaceae were found because of their small size. 

 Very few schizophyeeae were conspicuous in 1913, though the num- 

 bers of individuals were sometimes large and the total quantity suf- 

 ficient in late summer to give characteristic color to the waters. Baeil- 

 lariaceae w'ere always present and usually in large numbers. Many 

 of them are doubtless adventitious. Chlorophyceae were not j^rom- 

 inent, though some were present throughout the year. The conju- 

 gatae were not represented by many species and the numbers were 

 few. 



ZOOPLANKTON 



Almost all the zooplanktonts found were included in the three 

 groups Protozoa, Rotifera and Entomostraca. Other types of ani- 

 mals are decidedly rare. 



Amongst the Protozoa, Ciliata and Mastigophora predominate. 

 The group Mastigophora is meant to include the same organisms as 

 comprised under that head by Kofoid (1908), i.e., "all green and 

 brown flagellates, sometimes classified with the Chlorophyceae and 

 Phaeophyceae. " Rhizopoda were usually present but in small num- 

 bers. Heliozoa were rare except for one or two smaller forms which 

 kept up rather large totals for the group. Suctoria were rare. No 

 Sporozoa were recognized. Ciliata were distinctly more noticeable in 

 the dilute sewage of Stockton Channel than at either of the other 

 stations. 



The Rotifera were even more prominent inhabitajits of Stockton 

 Channel than the ciliate Protozoa, but their numerical superiority 

 may have been due to larger size and consequent capture by the net. 

 The numerical difference at the other stations was not very marked. 

 There is no question that their considerable size and large numbers 

 entitle them to the leading place among analytic organisms a.ssigned 

 by Kofoid (1908) to the Illinois Rotifera. The greater abundance in 

 the sewage laden water is, however, rather against his suggestion 

 that they may be found to be more characteristic of river than of 

 lake plankton. Local conditions indicate sewage or at least organic 



