North American FresJi-ivatcr Cyclopidce. 59 



three bristles. The inner one is a ciHate spine while the other 

 two are plumose setae. The middle one of the three is home 

 at the tip of a cone-shaped process. The inner edge of the 

 foot is bordered by a row of minute hairs. 



The rectptaciiliim semi n is (PI. XX., Fig. 2) is most peculiar 

 and characteristic. It consists of two parts, anterior and 

 posterior, separated by the suture marking the original division 

 of the first abdominal segment. The upper part consists of 

 two S-shaped canals, one on each side of the median line, 

 extending across the abdomen. The inner ends which point 

 downward, fuse in a thicker portion connecting the anterior 

 division with the posterior. The part of the receptaculum 

 behind the suture consists of two lateral sacs, which connect 

 with each other and with the upper part of the receptaculum 

 at the same point. In the middle of this common part is the 

 porus. The outer ends of the tubular portion are slightly 

 enlarged ; otherwise the diameter is uniform. The structure 

 of this organ has never before been observed in the American 

 representatives of Cyclops prasinus. 



The egg-sacs contain few ova and are closely adherent to 

 the abdomen. 



The length of the female varies from .48 to .7 mm. 



The color is unusually variable. The prevailing color of 

 European specimens seems to be green. I have seen l)oth 

 blue and pink individuals. Herrick says that the color varies 

 from deep indigo to greenish brown. 



Subgenus Paracyclops Claus. 

 Cyclops phaleratus Koch. (PI. XX., Fig. 3.) 



Cijclops phaleratus, Koch, '35-41, Ileft 21, pp. 8, 9. PJ. IX. 

 Cyclops jierarmatus, Crasin, '83, pp. 72, 73, PI. I., Fio;-. 9-l^i. 

 Cyclops phaleratxis, Selnueil, ■!)2. pp. 170-178, PI. VIII.. Fi^^. 1-11. 

 Cyclops phtileratus, Herrick and Turner. '95, pp. I'JO, 121. PI. XVII. , 



Fig. 1-7 ; XVIII., Fig. 2-2d ; XIX.. Fig. 1; XXI., Fig. 6-10. 

 Cyclops phaleratus, Marsh, "95, pp. 19, 20. 



DISTRIBUTION. 



In America this si^ecies is rare, though evidently widely 

 distributed. I have noted its occurrence in collections from 

 the Illhiois Eiver at Havana, 111. ; a pond at Urbana, 111. ; 



