Diaptomus Pseudoscmguineus Sp. Nov. 11 



two successive years, it is hoped to demonstrate the futil- 

 ity of drawing conclusions as to the nature of and the 

 reasons for the succession of life in inland waters with- 

 out spending years in accumulating accurate data. 



In one of the parks of St. Louis there is a lagoon-like 

 pond that is several hundred yards long. About three- 

 fourths of its length from one end is a strait-like con- 

 striction, the portion of the pond beyond this constric- 

 tion being at times of high water much shallower than 

 the remainder. During dry weather this portion gradu- 

 ally dries up. This shallow arm is the transitional pond 

 that is to be discussed. During the high waters of early 

 spring large areas of grass are submerged which die 

 after a certain length of time. From that time until the 

 pond dries up there is no vegetation higher than algae in 

 the water. The depth of the water varies from a few 

 inches to two feet, with mud bottom. The pond is ex- 

 posed to the sun during most of the day, the temperature 

 of the water ranging as high as 35°C and the hydro- 

 gen ion content varying from PH 7.2 to PH 8.2. The 

 record presented is for the spring and summer of 1920 

 and the spring and summer of 1921. 



Spring and summer 1920. — April 4. Water high; much grass sub- 

 merged; temperature 15 °C.; Simocephalus serrulatus Koch and Cy- 

 clops viridis (Jurine) var. insectus Forbes present in moderate num- 

 bers. 



May 5. Water high; grass growing in water; temperature 16°C.; 

 Simocephalus serrulatus Koch the dominant form; Cyclops viridis 

 (Jurine) var. insectus Forbes present in large numbers. 



May 20. Water high; grass abundant; temperature 22°C.; 

 Simocephalus serrulatus Koch the dominant form; Cyclops viridis 

 (Jurine) var. insectus Forbes and Bosmina longirostris (0. F. Mueller) 

 present in large numbers. 



May 22. Water high; grass dying; temperature 29°C.; Simoce- 

 phalus serrulatus Kock the dominant form, Bosmina longirostris (0. 

 F. Mueller) abundant, Cyclops viridis (Jurine) var. insectus Forbes 

 and Daphnia pulex (de Geer) present in small numbers. 



June 20. Water becoming shallow; no grass in pond; pond teem- 

 ing with animal life; Daphnia pulcx (de Geer) now the dominant form, 

 Cyclops viridis (Jurine) var. insectus Forbes, Bosmina longirostris 

 (0. F. Mueller) and Ceriodaphnia laticoiudata P. E. Mueller abund- 



