COPEPODA 



779 



95 (96) Furcae of variable length, armed externally with a row of fine 

 spines; very common. . Cyclops serrulalus Fischer i&s^- 



The long twelve- segmented antennae and the ser- 

 rate margined furcal rami serve to distinguish this 

 species. The figure of the abdomen shows the char- 

 acteristic structure of the furcal rami. There is a 

 good deal of variation in the form of the furca. 

 When serrulaius is hmnetic in habitat, the furcal 

 rami are long and slender; this form is known as 

 variety elegans Herrick. When it lives in pools or 

 littoral waters, the furcal rami are short and stout; 

 this form is known as variety montanus Brady. The 

 abdomen figured may be considered as typical of serru- 

 laius, elegans being much longer, and montanus corre- 

 spondingly shorter. Found everywhere the world over. 

 Length of female, 0.8 to 1.25 mm. 



B 



Fig. 1226. Cyclops semilatus. A, abdo- 

 men of female. X 67. B, fifth foot of 

 same. X 213. (Original.) 



96 (95) Furcae short, without lateral row of spines. 



Cyclops prasinus Fischer i860. 



It is a minute limnetic form. It resembles serrulaius in its long twelve- 

 segmented antennae, but its abdomen is very different. The furcal rami 

 resemble leuckarti in the fact that the lateral seta is placed at about mid- 

 way of the length, but the species is distinguished at a glance, not only by 

 its smaller size, but by the fact that the antennae are composed of twelve 

 segments. Cyclops prasinus is widely distributed, especially in the larger 

 bodies of water. It is common in the Great Lakes. 

 Length of female, 0.48 mm. 



Fig. 1227. Abdomen of female Cyclops prasinus. X 137. (Original.) 



97 (94) Fifth feet armed with one seta, swimming feet of two segments. 



Cyclops varicans Sars 1862. 



Cyclops varicans occurs in Panama and Guatemala, but there are no authentic records of its 

 occurrence in the United States. 



98 (77) Antennae composed of eleven segments or less 99 



99 (102, 103) Antennae composed of eleven segments 100 



100 (loi Rami of swimming feet composed of three segments. 



Cyclops phaleratus Koch 1838. 



This stout, dark-colored species is not uncommon in shallow lakes and 

 stagnant pools, and is readily recognized by the characters given in the key. 

 Length of female, 1.2 mm. 



Fig. 1228. Abdomen of female Cyclops phaleratus. X 69. (Original.) 



