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Cincinnati Society of Natural History. 



smaller than C. navus, which it resembles in the form of the 

 abdomen. The first segment is about three-fifths of the 

 whole cephalo-thorax. The second is shorter than the third. 

 The first abdominal segment equals the rest of the abdomen. 

 The furca are nearly as long as the three preceding segments, 

 and six or seven times longer than broad. The lateral spine 

 is at the last fifth. On the outer margin at the second fifth 

 are several minute spines. This point most readily charac- 

 terizes the species, The median setae are as two to three. 

 The first and fourth are short and nearly equal. 



The antennae are seventeen-jointed, and a trifle longer than 

 the first segment. The fifth foot is two-jointed, the first joint 

 being broader than long and bearing a long seta. The second 

 joint is a little longer than broad, and bears one short strong 

 seta and another nearly four times as long. This form can 

 be distinguished from that of C. navus by the greater elonga- 

 tion of the furca and the notched appearance on their outer 

 margin, due to the small spines. 



The armature of the terminal joint of the swimming feet 

 is the same as that of C. navus. 



The species is commonest in clear deep water, and is 

 probably pelagic. It is not very widely distributed, but is 

 usually abundant where it appears at all. 



Cyclops serrulatus Fischer. 



This species measures a little over i mm. The cephalo- 

 thorax is compact. The posterior margin of the last segment 

 is armed, laterally, with fine spines. The abdomen is slender 

 and long, the first segment being dilated anteriorly. 



The antennae are twelve-jointed. The last joints are in- 

 creasingly long and slender to the last, which is about as long 

 as wide. They reach nearly to the third segment. 



The caudal stylets are about five and a half times as long 

 as wide. Their outer margin is armed with numerous small 

 spines. The last segment of the abdomen is dentate posteri- 

 orly. The outer furcal seta is replaced by a strong spine, 

 serrate on its outer margin, and plumose interiorly. The 

 median setae are as 2 : 3. 



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