Marsh — North American Species of Cyclops. 1103 



of its length. The first and fourth of the terminal seta are 

 short and slender, the inner exceeding the length of the outer. 



The antennae (Plate LXXXI, fig. 2) have eleven segments, 

 the third and seventh being the longer. 



The swimming feet (Plate LXXX, figs. 1 and 8) are com- 

 posed of two segments. The spinous armature of the terminal 

 segments is 3, 4, 4, 3. 



The fifth foot (Plate LXXX, fig. 9) consists of a single seg- 

 ment. It is slender and bears at the tip a single seta. 



Average length of mature females ,5mm. 



Cyclops bicolor occurs in stagnant pools, and is widely dis- 

 tributed, although nowhere common. 



I have notes of a mature female with antennae of ten seg- 

 ments. In this female the egg sacs contained only four or 

 five eggs each while the more ordinary number is from fifteen 

 to twenty. 



This species, as described, does not correspond perfectly to 

 the diagnosis of bicolor as given by Schmeil. There is a dif- 

 ference in the form of the fifth cephalothoracic segment and 

 in the proportions of the furca. 



There is, apparently some variation in the position of the 

 fifth foot on the last cephalothoracic segment, and in some 

 individuals, it resembles somewhat rubellus of Lilljeborg. 

 The characters of the swimming feet, however, as given by 

 Lilljeborg make a clear cut distinction between rubellus and 

 bicolor. One might consider the American form a distinct 

 species. The differences are slight, however, and besides are, 

 for the most part, differences in structures which vary in 

 other species, so that it seems to me better to consider our 

 form as a variety of the European species. It may be added 

 that because of its comparative rarity, a large number of in- 

 dividuals have not been studied, and a larger amount of ma- 

 terial may show a closer relationship to the European form 

 than now appears. 



