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. 7 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 hears 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 furea. 
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. 
