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Cincinnati Society of Natural History. 



The apical spines of the fourth foot are equal in length. 

 The outer ramus of the first foot is so shortened as only to 

 reach the last joint of the outer ramus. The last of its spines 

 considered lateral is practically apical. 



It has been considered pelagic, and I have oftenest found 

 it in the deeper pools of clear water, but, with some marked 

 exceptions, the principal one being a marshy pond three 

 miles east of Milford. It is widely distributed and quite 

 common. 



Cyclops americanus Marsh. 



This is a large species of about 1.3 mm. The first seg- 

 ment is half of the cephalo-thorax. The first segment of the 

 abdomen equals the remainder. The last segment is dentate 

 posteriorly. The furcse are about five times as long as broad. 

 The lateral spine is at the last fifth. The median setae are 

 as three to four. 



The antennae reach the second segment. 



The fifth foot is two-jointed, the first being very broad. 

 It bears a long plumose seta. The second joint bears a very 

 short spine laterally and a long seta. Both joints are rounded 

 in their outline. 



The armature of the terminal joints of the swimming feet 



is as follows : 



Outer ramus. Inner ramus. 



Firstfoot .... ex. 3 spines 1 seta. 



ap. 2 setae 1 spine, 1 seta. 



in. 2 setae 3 setae. 



Second and ex. 3 spines 1 seta. 



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



in. 3 setae 3 setae. 



Fourth foot... ex. 3 spines..'... 3 setae. 



ap. 1 spine, 1 seta 2 spines. 



in. 3 setae 2 setae. 



This species is by far the commonest copepod near here. 

 Every little pool, even if it has only known a few days' exist- 

 ence, will be swarming with them. I have hardly found a 

 place where they were not present, and more than half the 

 time they are the most abundant form. They have no typical 

 color, but in most of my collections are red, or blue and red. 



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