263 



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 is 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 Fric 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 



