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Hydrographic conditions appear to affect C. albidus as they do 
other Entomostraca. In July-December, 1897, in stable low water 
the C. albidus population exceeds by over threefold that of these 
months in 1898. 
Of the totals of all records in 1894-1899, 74 per cent. are fe- 
males,—4 per cent. with eggs and 70 per cent. without,—and the 
remaining 26 per cent. are males. Immature forms and nauplii 
were not distinguished from those of other species. Egg-bearing 
females were recorded only in May and August—October, at times 
of maximum pulses. Over 82 per cent. of the males were found 
in August—October—a period of declining temperatures and decreas- 
ing food supply. 
This is a widely distributed species, though it seems generally 
to be present in relatively small numbers in the plankton. It occurs 
in many European lakes. Stenroos (’98) finds that it 1s the most 
abundant species of Cyclops in Nurmijarvi See, occurring in both 
the plankton and littoral fauna throughout the summer. Scourfield 
(98) finds it common in the waters of Epping Forest, where it is 
perennial in ponds and small lakes; and Burckhardt (’00) also finds 
it in the smaller lakes of Switzerland. 
It appears to be more generally reported from European streams. 
Thus, Schorler (’00) finds it to be rare in the plankton of the Elbe 
at Dresden in May; and Fri¢ and Vavra (’01), perennial in the 
littoral fauna of the same stream at Podiebrad, while Volk (’03) 
reports it in the plankton at four of seven localities examined at 
Hamburg. Meissner (’02 and ’03) finds it in May—August in the 
Volga at Saratoff, where it is abundant in the littoral zone or among 
vegetation and in quiet backwaters. 
Under a variety of synonyms this common and variable species 
has been reported from many American waters by Herrick (’84) 
and others. It was described by Professor S. A. Forbes (’90) as 
C. gyrinus, from the plankton of Lake Superior. With the exception 
of Marsh’s record (’95) from Lake St. Clair, it does not elsewhere 
appear to have been found in the plankton of the Great Lakes. 
Marsh (’93 and ’95) finds it generally in the plankton of smaller 
bodies of water in Wisconsin and Michigan, and E. B. Forbes (97) 
reports it as generally distributed in American waters of a permanent 
character. Brewer (’98) reports it (as C. signatus) in the vernal 
plankton of deep pools near Lincoln, Neb. No statistical 
