268 



lakes, backwaters of the Illinois at Havana. It is not, however, at 

 any time a factor of any importance in channel plankton of the 

 Illinois at Havana, being confined to the spring-fed lakes or those 

 shaded by vegetation, where regions of lower temperatures may be 

 found. 



This is a widely distributed form in the plankton of European 

 waters. Stenroos ('98) finds it abundant in the plankton of Nur- 

 mijarvi See, Scourfield ( '98) reports it as common in the waters of 

 Epping Forest in February-October, and Scott ( '99) as rare in that 

 of Scottish lakes. Fuhrmann ( '00) states that it is always rare in 

 Neuenburger See except in April, and is absent in November- 

 December, while Burckhardt ('OOa) finds it to be perennial in 

 Vierwaldstatter See, with breeding season in May-September and 

 maximum in August or September. 



It has been generally reported from European streams. Schorler 

 ( '00) finds it in the Elbe at Dresden in May-October, with greatest 

 numbers in July-September, and Volk ('03) reports it from four of 

 seven localities in the same stream at Hamburg, though Fric and 

 Vavra ( '0 1 ) do not find it at Podiebrad. Zykoff ( '03 ) , Zernow ('01), 

 and Meissner ('02 and '03) find it in the plankton of Russian rivers. 

 The last author states that it occurs in both channel plankton and 

 littoral fauna among vegetation where breeding females abound 

 during the maximum in May. The young only appear in the chan- 

 nel plankton. 



In American waters this species has often been held to include 

 C. edax, and the data here quoted from Birge and Marsh refer to the 

 combined species. Marsh ( '93 and '95) finds it generally distributed 

 in the lakes of Michigan and Wisconsin, and in the plankton of 

 lakes Erie, Michigan, and St. Clair. Birge ('97) finds it in the 

 summer plankton of Lake Mendota, where it is even more abundant 

 than C. viridis var. brevispinosus. 



Cyclops modestus Herrick was recorded in channel plankton 

 only in November, December, and March, in small numbers and 

 isolated occurrences at temperatures of 41 and below. E. B. 

 Forbes ('97) states that this species lives in shallow, weedy water, 

 and has never been found in large numbers, though widely dis- 

 tributed. On account of its relative rarity it may have been over- 

 looked by me and have a wider seasonal distribution than my 

 scanty data indicate. 



