118 Illinois State Laboratory of Natural History. 



segment as long as remainder of abdomen, dilated, 

 armed with small spines ; second segment very short ; 

 third segment longer than f ureal rami. Antennae 

 extending to furca. franciscanus. 



21 (20). Third segment of outer ramus very indistinct or 



aborted ; armed with two short subequal spines. Second 

 segment of outer ramus about as long as the first, hairy 

 within and without. Inner ramus reaching about to 

 end of first segment of outer ramus, hairy, armed with 

 two long hairy subequal spines. First abdominal seg- 

 ment shorter than remainder of abdomen, dilated but 

 unarmed; second segment shorter than the third, 

 which is longer than the furca. Antennae not reaching 

 end of furca. piscinae, 



22 (19). Outer ramus 2-segmented. 



23 (26). Second segment of outer ramus armed with a spine 



in addition to the two spines representing the third 

 segment. 



24 (25). Terminal spines of inner ramus hairy, nearly half as 



long as ramus, which reaches to the end of the first 

 segment of the outer ramus. Second segment of outer 

 ramus shorter than the first, slightly curved, denticulate 

 within ; third segment represented by two spines, the 

 inner hairy, about half as long as the outer, which is 

 smooth. First abdominal segment longer than re- 

 mainder of abdomen ; second segment shorter than 

 third; the third longer than furca. Antennas reaching 

 tip of furcal rami. lintoni. 



25 (24). Terminal spines of inner ramus hairy, not nearly 



half as long as ramus, which is hairy at the apex. Third 

 segment of outer ramus represented by two spines, the 

 inner about twice as long as the outer. Second seg- 

 ment armed with a small spine. Last thoracic seg- 

 ment greatly produced laterodorsally ; armed on each 

 side with two small spines. First abdominal segment 

 about as long as remainder of abdomen and armed 

 with two large spinose processes ; second segment 



