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Cyclops phaleratus Koch was recorded in channel plankton only 

 in small numbers in November-December, 1897, at minimum tem- 

 peratures. E. B. Forbes ('97) states that it is a littoral form, 

 confined to marginal vegetation. 



Cyclops prasinus Fischer. Average number, 2. This species 

 occurs sparingly and irregularly in September-March in channel 

 plankton, appearing in largest numbers in the early autumn of 1895 

 and most continuously in the winter of 1898-99. The numbers are 

 always small, never reaching 400 per m. 3 , and in 12 of the 17 records 

 falling below 100 per m. 3 The percentage of collections containing 

 C. prasinus in the totals rises above 20 per cent, only in December 

 (24 per cent.). The seasonal distribution in channel plankton 

 indicates a limitation to the colder part of the year, all records but 



5 being below 40. Nevertheless, in September-October, 1895, the 

 species was recorded in 56-79. This fact and its relatively small 

 numbers generally, make it probable that inferences from our 

 scanty data concerning its seasonal distribution can not be con- 

 clusive. 



Of the totals in all years, 86 per cent, are females without eggs, 



6 per cent, females with eggs (found in February and November), 

 and 8 per cent, males. 



E. B. Forbes ('97) finds the species widely distributed in 

 American waters from the Great Lakes to roadside pools. Marsh 

 ('93 and '95) finds it (as C. fluviatilis} in the larger bodies of water 

 in Wisconsin and Michigan, and in lakes Erie, Michigan, and St. 

 Clair. In Green Lake he ('97) finds it to be the most abundant 

 species of Cyclops, and perennial, with maxima in September- 

 November. His statistical data exhibit somewhat irregular numbers 

 which contain suggestions of recurrent pulses such as appear in 

 our records of other species of Cyclops. Brewer ('98) finds the 

 species in the plankton of pools near Lincoln, Neb. 



Cyclops serrulatus Fischer. Average number, 3. This species 

 was taken sparingly in channel plankton, exhibiting only isolated 

 occurrences in December, January, March, and May, in flood waters 

 at temperatures of 32-75. It is much more abundant in Spoon 

 River, where it is sometimes the dominant species of the genus, 

 appearing in May-September, and in small numbers in colder 

 months. It appears to be adventitious in channel plankton of the 

 Illinois River. 



