58 Illinois State Laboratory of Natural History. 



It is thus, in all probability, quite generally distributed 

 over the eastern and central United States, but I have not 

 found it in collections from the far AVest. It occurs in all 

 situations from great lakes and rivers to temporary roadside 

 puddles of but a few weeks' duration. 



SPECIFIC DESCRIPTION. 



This minute species has a slender cephalothorax which is 

 very nearly elliptical in outline. The first segment is regu- 

 larly convex anteriorly and is unusually long. The posterior 

 borders of the segments are entire. The lateral edges of the 

 last segment are fringed by a row of the finest hairs. 



The abdomen is long and slender and tapers but little. 

 The enlargement of the anterior segment is slight. The pos- 

 terior borders of all the abdominal segments are very finely 

 serrate. The stylets are short and divergent but are not 

 themselves outcurved. The lateral spine is inserted just 

 beyond the middle of the stylet. The inner and outer apical 

 bristles are very short and delicate, the inner one, the longer 

 of the two. Only the middle pair of setae are well developed, 

 and the outer of these is three fourths the length of the inner. 



The first pair of antennae (PI. XIX., Fig. 2) of the female are 

 twelve-segmented and often reach quite to the first abdominal 

 segment. The seventh, eighth, and ninth segments are very 

 long. The last three segments are curved and the last four are 

 freely movable. Schmeil states that the ninth segment bears 

 a sense-club. I do not find it present in the American repre- 

 sentatives of the species, although there is a minute sensory 

 bristle on the end of the tenth segment. The last three seg- 

 ments bear a hyaline plate whose edge is entire. 



The spines and setae of the three- segmented swimming feet 

 are very long and slender. The armature is as follows : — 

 First pair : outer ramus, three spines, five seta' ; inner ramus, 

 six setae. Second pair : outer ramus, four spines, five setae ; 

 inner ramus, six setae. Third pair armed like second. Fourth 

 pair: outer ramus, three spines, five seta-; inner ramus, 

 one seta, one spine, three setae. 



The fifth foot (PL XX., Fig. 1) is one-segmented and bears 



