67 



shifting in the position of the maxima. Thus the pulse of January 

 25, 1898, appears after a 3 5 -day interval, but in the midst of the 

 rising winter flood, to whose effect the delay may be attributed. 

 In both 1896 and 1898 the 28-day rhythm is interrupted at the time 

 of the vernal pulse in April-May. It appears as though these re- 

 current pulses -if such exist were submerged in the greater ver- 

 nal increase. The double summit of the vernal pulse in the curve 

 of the Bacillariacea and Mastigophora (PI. II.) for 1898 suggests the 

 compound character of this pulse in the case of these groups of 

 organisms at least. The time interval in the case of the vernal in- 

 terruption is also significant. In 1898 there are two pulses between 

 March 22 and July 19, at intervals of 42 days a total of 84 days, 

 which is the equivalent in duration of three 28-day intervals. 



The total number of species of Mastigophora recorded by me 

 from the plankton of the Illinois River is over sixty. This number 

 will be increased to more than seventy if forms not separated in our 

 enumerations be distinguished as separate species. 



The Protomastigina (including the Bicoscecidce and the Cras- 

 pedomonadida] are well represented in the plankton by passive 

 limnetic species which are principally sessile on other planktonts. 

 These are Bicosoeca lacustris, Salpingceca brunnea, S. minuta, and 

 Diplosiga frequentissima. Asterosiga radiata is a eulimnetic repre- 

 sentative and Anthophysa vegetans an adventitious one. As a group 

 they are more abundant during the warmer part of the year. 



The Chrysomonadidcz are also well represented, and include the 

 most abundant flagellates of the plankton of the colder months. 

 Synura uvella is quantitatively the largest factor furnished by this 

 group. It is supplemented by Syncrypta volvox, and the various 

 forms of Dinobryon, Uroglena, and Mallomonas. The last two 

 genera have more of a summer range of occurrence, but are not of 

 quantitative importance in the waters of the Illinois. 



The CryptomonadidcB are represented only by Chilomonas and 

 Cryptomonas, and are of somewhat constant, though of minor, 

 importance quantitatively. 



The Euglenidce, on the other hand, are, in our waters at least, 

 second to no coordinate group in their quantitative importance. 

 They are individually of relatively large size, and they occur in 

 great numbers throughout the summer months, replacing the 

 Chrysomonadida of the colder seasons of the year. Euglena 



(6) 



