1080 Wisconsin Academy of Sciences, Arts , and Letters 
The antennae consist of 17 segments. Richard (Richard 
1891) and Steuer (Steuer ’97) have shown that the number of 
antennal segments varies in the European forms, but I have not 
found this to be true in my American collections. The anten¬ 
nae vary somewhat in length, reaching about to the end of the 
first cephalothoracic segment, but they may fall short of this 
length or exceed it. The twelfth segment bears a sensory club. 
The setae arming the segments are rather short. 
The spinous armature of the terminal segments of the swim¬ 
ming feet is 2, 3, 3, 3. 
The fifth foot (PI. LXXIII, figs. 10 and 11) consists of two 
segments. The breadth and length of the first segment are 
about equal; it bears on its outer distal angle an elongate plu¬ 
mose seta. The second segment is commonly twice as long as 
broad, but it may be still more slender; on its outer distal 
angle it bears an elongate and plumose seta, on its inner distal 
angle it bears a spine like seta which is less than half the 
length of the outer seta. This inner seta may be serrate as 
in the European forms, but neither the serration of this seta 
nor the plumose character of the other setae is very commonly 
seen in our American forms. The outer seta is borne upon 
a process of the segment, the outer margin of the segment 
being longer than the inner. 
The size is somewhat variable, the American forms, ap¬ 
parently, being smaller than those found in Europe. The fe¬ 
male is commonly about 1.1 mm. in length but may be not 
more than .95 mm. 
C. bicuspidatus is found in all our northern states north of 
the Ohio river, and has been collected as far north as the 
Saskatchewan. 
Generally speaking those found as limnetic forms have an 
elongated form, while those in shallow bodies of water and 
pools are shorter. Herrick’s navus (PI. LXXIX, fig. 11) is an 
example of this short form. There is no doubt that navus is 
simply a variety of bicuspidatus for I can verify the state¬ 
ment of Forbes that all intermediate forms can be found. 
Bicuspidatus is the common limnetic form of the Great Lakes,, 
and in its elongated form is common in other deep lakes*. 
