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 Chlorophycee, the Bacillariacee, or the synthetic 
Mastigophora. 
DISCUSSION OF SPECIES OF SCHIZOPHYCE#£. 
Anabena sptroides 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 e@ruginosa (Kiutz.) 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., Pl. 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, 
