5 Illinois State Laboratory of Natural History. 



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segment is very large and is twice as long as the remaining 

 segments together. The posterior edges of all the segments 

 are smooth. 



The abdomen is relatively small, but is broad in proportion 

 to its length. It tapers but little and the first segment is 

 scarcely at all enlarged. The segments, except the last, are 

 finely and irregularly notched posteriorly. The caudal stylets 

 are short, the length to the breadth being about as three to 

 one. They are not ciliate within. In the small number of 

 specimens which I have had an opportunity to examine there 

 is no outer lateral spine, but at the usual place for this spine, 

 a little behind the middle, is a shallow scar where a spine 

 might at some time have been attached. I do not think, 

 however, that this is probable. The terminal setae are all 

 well developed, but the median pair is much longer than the 

 lateral ones. The innermost seta is slightly longer than the 

 outermost. Of the four, the second from the inside is the 

 longest. 



The first antenna' of the female are seventeen-segmented 

 and reach to the middle or end of the second cephalothoracic 

 segment. The twelfth segment bears the usual seta and 

 sense-club, though the latter organ is unusually small. The 

 fourteenth segment bears an especially long, strong seta. 

 The last two segments (PI. XV., Fig. 1) bear a narrow hyaline 

 lamella which projects some distance beyond the end of the 

 seventeenth segment. The edge of this plate is entire. Of the 

 last three segments, the middle one (sixteenth) is the longest. 



The seta? of the swimming feet are short and stout. The 

 armature is as follows : — First pair : outer ramus, three 

 spines, five seta? ; inner ramus, one seta, one spine, four 

 seta?. Second and third pairs : outer ramus, four spines, five 

 seta? ; inner ramus, one seta, one spine, four seta?. Fourth 

 pair : outer ramus, three spines, five setae ; inner ramus, 

 one seta, two spines, two setae. 



The fifth feet (PI. XV., Fig. 2) are one-segmented and bear 

 one strong spine and two seta' each. The spine is about one 

 third the length of the seta?. The inner seta, that is the one 

 next the spine, is borne on a conical projection from the 



