32 Illinois State Laboratory of Natural History. 



not markedly divergent, and there is no conspicuously broad 

 space between their points of attachment. The outer apical 

 seta is delicate and as long as the stylet. Of the remaining 

 three, all of which are well developed, the middle one is the 

 longest and the innermost the shortest. 



The first antennae are long and slender, terminating at the 

 middle or end of the third cephalothoracic segment. The last 

 two segments are both long, but the sixteenth (penultimate) 

 is the longer of the two. These two segments bear broad 

 hyaline plates (PI. VIII., Fig. 2). The margin of the one 

 borne by the sixteenth segment is entire, but the one on the 

 following segment besides being finely serrate its whole length 

 is deeply notched near its distal end. This notch is very 

 characteristic of the species. On the twelfth segment is the 

 usual sense-club. 



The posterior border of the second segment of the outer 

 maxillipeds usually bears a series of rounded transverse 

 ridges, which extend in a series from the proximal end of 

 the segment nearly to the other end. The presence of this 

 structure seems characteristic of the European form, but may 

 rarely be entirely absent in American specimens. 



The setae and spines of the swimming feet are conspicuously 

 long and strong. The margin of the connecting lamella of 

 the fourth pair of feet bears a pair of sharp teeth. The 

 feet are armed as follows: — First pair: outer ramus, two 

 spines, four seta? ; inner ramus, one seta, one spine, four setae. 

 Second and third pairs : outer ramus, three spines, three 

 seta'; inner ramus, one seta, one spine, four setae. Fourth 

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

 one seta, two spines, two seta-. 



The rudimentary foot (PL VIII., Fig. 3) is two-segmented. 

 The basal segment is short and roughly quadrate, with a long 

 plumose seta borne on its outer angle. The distal segment is 

 long and slender. On the middle of the inner side is borne a 

 long pectinate spine, and at the tip a seta of about equal length. 



The receptaculum seminis is large and elliptical, and the 

 anterior part, from which proceed the canals, is laterally 

 expanded. 



