Copepoda Found in the Vicinity of Lincoln, Nebraska. 135 



The fifth foot is one jointed. It bears a seta on its outer side, 

 a terminal seta, and a strongly serrate spine on its inner side. 



The armature of the feet is not necessary for the identifica- 

 tion of this form, as there is no other form resembling it 

 which has different armature. All the spines are very 

 strongly serrate. 



This species is widely distributed and numerous, but not 

 nearly as common as C. americanus . The variety, elegans, 

 seems to be quite distinct. I have found the two together 

 i only once or twice, though they are both quite common. 



It differs from the type in the greater elongation of the 

 antennae, the first cephalo-thoracic segment, furca, and median 

 furcal setae. The antennae reach the fourth segment and are 

 stronger than those of the type. The furcae are eight times 

 as long as broad. The long caudal setae may make the 

 species 2 mm. The setae are more closely plumose, or rather 

 spinous than in any other species. 



Cyclops fluviatius Herrick. 



One of the smallest species in the genus. It is easily rec- 

 ognized by its twelve-jointed antennae, which reach nearly to 

 the abdomen. The striking characteristic of the female 

 antennae is the elongation of the seventh, eighth, and ninth 

 joints, particularly the eighth. The appearance of the antennae 

 justifies Herrick's comparison to the Diaptomi. 



The first segment is considerably more than half of the 

 cephalo-thorax. The last thoracic segment is narrower than 

 the first abdominal. The abdomen is slender and the furca 

 very short, being only a little longer than the last abdominal 

 segment. The two median furcal setae are equal, or as 4: 5. 



The fifth foot is one jointed and shaped much like that 

 of C. serrulatus . It bears three setae. While in almost every 

 other particular the species agreed with Herrick's description 

 and drawings, the form of the fifth foot was entirely differ- 

 ent. I could not see that the setae were plumose or serrate, 

 while Herrick makes them very distinctly so. 



The ovisac usually contains only five or six ova. 



The swimming feet, like the antennae, resemble the same 

 in the Diaptomi. Their armature is as follows : 



17 



