38 Illinois State Laboratory of Natural History. 



internally. In the smaller forms most closely related to 

 viridis, in which the small spine of the fifth foot is always 

 separate from the segment, the inner border of the stylet is 

 never filiate, though in rare cases the whole inner aspect of 

 the stylet seems to be set with the shortest of hairs, only 

 visible on account of their points of attachment. 



The first species closely related to viridis described in 

 America was C. insectus, described in 1882 by Dr. Forbes. 

 Later in the same year C. L. Herrick described a very closely 

 related form under the name of C. parens. This species has 

 been most profusely figured by Herrick, but his drawings of 

 the fifth foot are so very different as to make it impossible to 

 say where it belongs in this most perplexing group. I have 

 failed in my attempts to obtain authentic examples of ( '. 

 parens, but have found a few specimens answering to Herrick's 

 description in a temporary pond in Urbana, Illinois. I can- 

 not, however, vouch for their identity. In the same collec- 

 tion I found other specimens differing from those above men- 

 tioned only in the presence of the additional spine of the first 

 and fourth feet — the feature separating this form from C. 

 insectus. 



So variable is C. insectus, found, as it is, in an endless vari- 

 ety of situations and localities, that the lack of a single spine 

 on the distal segment of the outer ramus of the first and 

 fourth feet is. not sufficient ground for the distinction of even 

 a variety, for I find, as does Dr. Schmeil, that the armature 

 of the swimming feet is not in all species absolutely con- 

 stant. 



In Herrick and Turner '95 (PI. XXXIY., Fig. 5), is a draw- 

 ing of the fifth foot of ('. parens. This drawing was evidently 

 made with somewhat greater care than were those on Plates 

 XX. and XXL, and represents approximately the same ap- 

 pendage in ('. insectus. 



Cyclops amerieanus, described by C. I). Marsh in 1892, 

 proves on examination of authentic examples to be synony- 

 mous with C. insectus. Undoubtedly C. amerieanus of Herrick 

 and Turner is identical with Marsh's form and is consequently 

 also a synonym of insectus. 



