4'2 Illinois State Laboratory of Natural History. 



Cychps parcus, Marsh, "93, pp. 208, 209. PJ. IV.. Fig. Ki: V.. Fig. 1. 

 Cyclops americanvs, Eerrick and Turner, '95, pp. 91, 92, PI. XIV.. 



Fi<;. 1-9. 

 Cyclops parcus, Herriek and Turner. '95, pp. 03, 94, PJ. XX.. Fig. 



12-15: XXI.. Fig. 22: X X 1 1 1.. Fig. 8 : X X X .. Fig. 1-8. 



This variety represents in America the smaller members of 

 the viridis relationship. It is distinguished from viridis in 

 Europe by the lack of cilia on the inner side of the stylets, 

 by some slight differences in the shape of the receptaculum 

 seminis (PI. XL, Fig. 3), and by the different shape of the fifth 

 foot. The receptaculum seminis differs in that the upper part 

 is larger in proportion to the segment in insectus and is some- 

 what different in outline. In the fifth foot (PI. XL, Fig. 4 

 and 5), the outer distal angle of the basal segment is much 

 less produced and the spine of the distal segment, which is 

 always separated from the segment by a suture, varies in 

 length from a minute barbule to a long heavy spine, longer 

 than the segment itself. The armature of the swimming feet 

 (PI. XL, Fig. 6) is not constant and is not in C. viridis useful 

 even as a varietal distinction. 



This brief diagnosis includes under the varietal name 

 insectus, forms which differ superficially to a marked degree, 

 but after continuous work for more than a year with very 

 large collections from all parts of the United States I have 

 been forced to throw ^hem all together for the simple reason 

 that there is no one set or combination of characters suffi- 

 ciently invariable to subdivide the group. 



The antenna^ of this variety usually terminate at or before 

 the end of the first cephalothoracic segment, but in examples 

 from Alturus Lake, they reach the middle of the second seg- 

 ment. 



The stylets of this variety vary considerably in proportions. 

 The following series of measurements of nine specimens 

 shows the extent to which this character varies. On the left 

 is a list of the localities from which the specimens were 

 obtained and on the right are figures representing the propor- 

 tion between the length and breadth of the stylet. 



