Copepoda Found in the Vicinity of Lincoln, Nebraska. 129 



is sharply bent to almost a right angle. Its tip is bent back- 

 ward a little. The claw is very finely serrate. 



The right foot and claw is usually bent round the left foot, 

 which reaches to about the second third of the terminal 

 joint of the right foot. The inner ramus of the left foot 

 reaches the middle of the terminal joint of the outer ramus. 

 Both of the terminal joints of the outer ramus are hairy on 

 their inner aspects. The terminal one has a curved spine on 

 the inner face and a small blunt projection at its tip. 



This species was found but once. It was present in a 

 temporary very shallow pool which covered half an acre. 

 The greatest depth of the pond was not more than two feet. 

 It was found there April 24 and May 15, but had disappeared 

 May 29, when the water had become so shallow that the 

 Birge net could hardly be used. 



Key to the species of Cyclops found. 



A. Antenna ij-jointed. 



a. Fifth foot two-jointed, basal joint longer than broad. 



signatus. 



b. Fifth foot two-jointed, basal joint nearly square. 



leuckarti. 



c. Fifth foot two-jointed, basal joint broader than long. 



1. Terminal joint bearing a long seta and very short spine. 



americanus. 



2. Terminal joint bearing two setae, and nearly three times 

 as long as its breadth at the base. navus. 



3. Terminal joint bearing two setae, and not twice as long 

 as its breadth at base. pulchellus. 



B. Anten?icB 12-jointed. 



a. Furca armed externally with small spines, serrulatus. 



b. Furca shorter and not so armed. fluviatilis. 



Cyclops signatus Koch. 

 (tenuicornis and coronatus Herrick). 



The largest species of Cyclops found here. It varies from 

 1.4 mm. to 1.8 mm. Its structure is well known. The first 



1 L 



