20 



ton, were not found in our fluviatile environment. This group 

 contributes to the water-bloom, contains a number of adventitious 

 planktonts, and is one of the primal sources of the food supply. 

 In our waters it seems to be quantitatively much less important 

 than either the Chlorophycea, the BacillariacecE, or the synthetic 

 Mastigophora. 



DISCUSSION OF SPECIES OF SCHIZOPHYCE^E. 



Anabozna spiroides Klebahn.* Average number, 637,692 (silk 

 15,431). In the water-bloom from the last of June till the end of 

 October. Not noted in 1898, but not infrequent in 1897 a low- 

 water year. Temperature range, 60-89. Data insufficient to 

 determine maximum. Largest number recorded, 7,200,000, June 

 28. 



Clathrocystis ozruginosa (Kutz.) Henfr. Average number of 

 colonies or masses, 83. More abundant in the previous low- water 

 year. From May till the end of November in the water-bloom. 

 Predominantly a midsummer species. Maximum in August and 

 September (108,000) . Confined principally to the low water of mid- 

 summer, appearing when the water reaches a temperature of 70, 

 and reaching its maximum development in temperatures above 

 this point, declining at once to small numbers (less than 1,000) 

 when the temperature falls below 60, but lingering till the water 

 approaches the freezing point late in November. 



Merismopedia glauca (Ehrbg.) Nag. Average number of col- 

 onies, 93. In 1897, 889,412.* In the water-bloom. Recorded 

 from July till the end of October, and also singly in January and 

 February. It was more abundant in 1897 than in 1898, and the 

 maximum number (15,840,000*) appeared on August 31. 



Microcystis ichthyoblabe Kutz.* Average number, 83,059,615. 

 Recorded in all collections throughout the year, except in some 

 flood waters of February and March, when the silt probably ob- 

 scures it. Minimum numbers (less than 50,000,000) prevail during 

 cold months, November to April, when the temperature ranges 

 from 32 to 50. A well-sustained pulse exceeding 200,000,000 

 appears with the volumetric plankton maximum of April-May 

 (Pt. I., PI. XII.) and declines to the previous minimum with the 

 falling off in the plankton. The maximum pulse appears later, in 

 August and September in 1898, in September and October in 1897, 



