Marsh — North American Species of Cyclops. 1081 



•although it is not confined to them. I have already discussed 

 (Marsh 1903) its occurrence in Wisconsin lakes. It seems to 

 prefer cold water, and my work in Wisconsin seemed to show 

 that it might be considered as preeminently a winter form. 



Miss Pratt (Pratt 1898) finds it a winter form in Lake 

 Bassenthwaite in England. I have found it in small bodies 

 of water in Indiana in the winter, while in the cold lakes of 

 the Rocky Mountains it is a summer form. 



Birge and Juday, in a recent paper (Birge and Juday 

 1908) have noted an interesting fact in the life history of 0. 

 bicuspidatus. In certain of the Wisconsin Lakes, in the sum- 

 mer season it is found in large numbers in a resting stage 

 ■enclosed in a cocoon, hatching out in the fall. The authors 

 find themselves unable to correlate this cocoon stage with 

 either changes of temperature or oxygen content of the water. 

 It would seem to us from our knowledge of the habits of the 

 species, that it is probable that temperature will be found to 

 he the controlling cause of this encystation. 



CYCLOPS LEUCKARTI Claus. 

 Plate LXXIV, figs. 4-11; Plate LXXV, figs. 1-3. 



1857. Cyclops Leuckarti Claus, p. 35, pi. I, fig. 4, pi. II, figs. 13 and 14. 

 1863. " " Sars, p. 239. 



1863. " " Claus, p. 101. 



1874. " simplex Poggenpol, p. 70, pi. XV, figs. 1-3. 



1875. " tenuicornis Uljanin, p. 30, pi. IX, figs. 12 and 13. 

 1876a. " Leeuwenhoekii Hoek, p. 19, pi. Ill, figs. 1-12. 

 1876b. " Leeuwenhoekii Hoek, p. 132, pi. VII, figs. 1-12. 

 1880. " simplex, Rehberg, p. 542. 



1884. " " Herrick, p. 150. 



1884. " oithonoides Herrick, p. 150, pi. S, figs. 2-6. 



1884. " Leuckarti Herrick, p. 146. 



1885. " " Daday, p. 218. 

 1885. " simplex Daday, p. 236. 



1885. " pectinatus Daday, p. 223, pi. I, figs. 7-13. 



1886. " simplex Vosseler, p. 193, pi. IV, figs. 15-17. 



1887. " " Herrick, p. 17, pi. VII, fig. 1, a-j. 

 1890. " " Thallwitz, p. 79. 



1890. " " Lande, p. 55, pi. XVI, figs. 42-45, pi. XVII, figs. 



46-50, 



