270 



This widely distributed Cyclops appears but rarely in the records 

 of the plankton of European lakes, and then only in the smaller 

 ones. Stenroos ('98) reports it as abundant in the littoral zone of 

 Nurmijarvi See; and Scourfield ('98) finds it perennial and the 

 most abundant species of Cyclops in the waters of Epping Forest. 



On the other hand it has been found generally in the plankton 

 of European streams. Zimmer ('99) finds it in the Oder, and 

 Schorler ( '00) states that it is abundant in April- June in the plank- 

 ton of the Elbe at Dresden ; Fric and Vavra ( '01) find it only in the 

 littoral fauna at Podiebrad; and Volk ('03) in the plankton in four 

 of seven localities in the Elbe at Hamburg. Sowinski ( '88) found 

 it in the plankton of the Dnieper, Rossinski ('92) in that of the 

 Moskwa, Zykoff ('00) in the summer plankton of the Volga, and 

 Zernow ('01) in the winter plankton of the Schoschma. Meissner 

 ( '02 and '03) reports it in May- August as not abundant in the back- 

 waters and vegetation of the Volga at Saratoff. 



In American waters Marsh ('93 and '95) finds it in smaller lakes 

 of Wisconsin and Michigan but not in the Great Lakes, and E. B. 

 Forbes ('97) states that it is one of the most common and widely 

 distributed species in American waters. It appears, however, not 

 to be quantitatively an important element in lake or river plankton. 

 Brewer ('98) finds it to be the most abundant vernal Cyclops in the 

 small bodies of water near Lincoln, Neb. 



Cyclops viridis Jurine. A synonymy and a discussion of varia- 

 tions in this the dominant and most variable of all the Cyclops in 

 our channel plankton, has been given by E. B. Forbes ( '97). I have 

 grouped the individuals in our plankton under two varieties, 

 brevispinosus Herrick and insectus Forbes. The two varieties inter- 

 grade, and in my separation I have followed only a single character 

 readily visible without dissection or manipulation, namely, the 

 outer terminal spine of the stylet, which is short, broad, and lance- 

 shaped in brevispinosus, and more spine-like in insectus. Judging 

 from the results of this method of separation, it appears that this 

 lance-shaped spine is a character of the male in many instances, 

 though not found in all males or limited to this sex. 



Cyclops viridis var. brevispinosus Herrick. Average number, 

 124; in 1897, 447; in 1896, 622; in 1895, 850; and in 1894,68. This 

 form occurred in all months but January, but predominantly from 

 the last days of April to the first week in October, the percentage 



