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 (00a) 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 Fri¢ and 
Vavra (’01) do not find it at Podiebrad. Zykoff (’03), Zernow (’01), 
and Meissner (’02 and ’03) find it in the plankton of Russizn 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. Buirge (’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. 
