Copepoda Found in the Vicinity of Lincoln, Nebraska. 131 



Cyclops leuckarti Sars. 



This is a large species and the most variable in size. Speci- 

 mens collected at the same time and place may vary from 1 

 mm. to 1.5 mm. Herrick gives the variation as from 0.5 to 

 1 mm., a marked difference in size. The specimens found 

 here agree most closely with his "deep-water variety." The 

 species is quite slender, the cephalo-thorax not being as dis- 

 tinctly marked off from the abdomen as is usual. The first 

 segment is equal to half the cephalo-thorax and almost equal 

 to the abdomen. The last three segments of the abdomen 

 are pectinate posteriorly. The caudal furcae are strongly 

 divaricate, and nearly equal in length to the two preceding 

 segments. The lateral spine is at the end of the third fifth. 

 The species is most readily recognized by the three well- 

 developed setae. The inner terminal seta is two-thirds the 

 length of the inner median, and the two median are nearly 

 equal. These three setae, in rare individuals, are so closely 

 plumose as to give something the appearance of the setae of a 

 Diaptomus. These individuals can be readily recognized by 

 the naked eye. 



The fifth foot is two-jointed. The first joint is nearly 

 square and bears a short plumose seta. The second joint 

 bears on its inner side a long seta serrate on one side, and 

 at its tip an equally long seta plumose for its last third. The 

 antenna is seventeen-jointed and reaches the middle of the 

 third segment. The terminal joint is armed with a toothed 

 hyaline plate. These teeth become plain only with high 

 power. 



The armature of the terminal joints of the swimming feet 



is as follows : 



Outer ramus. Inner ramus. 



Firstfoot.... ax. 2 spines 1 seta. 



ap. 2 setae 1 spine, 1 seta. 



in. 2 setae 3 setae. 



Second and ex. 2 spines 1 seta. 



Third feet.... ap. 1 spine, 1 seta 1 spine, 1 seta. 



in. 3 setae 3 setae. 



Fourth foot.. . ex. 2 spines 1 seta. 



ap. 1 spine, 1 seta 2 spines. 



in. 3 setae 2 setae. 



13 



