1080 M f isconsin 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 

 pimply a variety of bicuspidatus for I can verify the state- 

 ment of Eorbes 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, 



