40 Illinois State Laboratory of Natural History. 



proportional lengths are not entirely constant. Usually the 

 smaller of the two is as long as the abdomen, and the larger 

 exceeds it in length. They are often of exactly the same size, 

 and often the difference is considerable. 



" The first antennae are seventeen-segmented, usually reach- 

 ing l)ack only to the posterior border of the first cephalo- 

 thoracic segment. The last three segments are but little 

 longer than those immediately preceding. The twelfth seg- 

 ment bears a projecting sense-club, 



"The remaining pairs of ai)pendages, with the exception of 

 the rudimentary feet, present no notable characters and hence 

 are systematically valueless. Spinous armature of swim- 

 ming feet, 2. 3. 3. 3. 



"The rudimentary foot (PI. X., Fig. 2) is two-segmented. 

 The extraordinarily l)road basal segment bears on the lower 

 outer angle a long plumose hair. On the lower border, 

 immediately at the inner angle of this segment, is attached 

 the relatively small distal segment, which bears at its distal 

 end a plumose hair and at the inner margin a very minute 

 spine.* 



"The rt'ccjitoniliiiii scmiiiis (PI. X., Fig. 3), the two small 

 lower divisions of which terminate in the lateral canals, are 

 usually covered by the larger, more or less heart-shaped upper 

 division. Exact knowledge of the structure of this organ is 

 usually first possible after the application of delicate pressure. 



" The large elliptical egg-masses stand oft' from the abdomen 

 at a very sharp angle. 



" The color is usually a dirty green, seldom a light brown. 

 In a pool in Diemitz I met with quite fire-red examples. 



" The size is very variable. With iiulividuals 1 . 5-2 mm. one 

 finds others 2.5, 3, 4, or even 5 mm. in length. 



" The clearest and simplest recognition characters are the 

 rudimentary feet and the structure of the rrrcjttociiJiiiit 



*Iii a foot-note Schmeil states that cHaus, Hoek, Richard, and Land6, consider 

 this spine as a process of the segment, that Ulianin figures it as separated from the 

 segment by a suture, and that he, Schmeil, liad o1)served it both ways. 



