North American Species of Diaptomus. 115 



long as wide, hairy within. Antenna? extending barely 

 to base of abdomen. stagnalis. 



4 (3,7). Inner ramus indistinctly 2-segmented. 



5 (6). Terminal spines of inner ramus about half as long as 



ramus. Second segment of outer ramus armed with a 

 single spine. Two spines on the third segment ; suture 

 between this and preceding segment indistinct. Inner 

 ramus extending beyond middle of first segment of 

 outer ramus ; armed at apex with two long spines. 

 Third segment of outer ramus armed with two very 

 large stout spines, the inner hairy, less than twice as 

 long as the outer. First abdominal segment longer 

 than remainder of abdomen ; armed anteriorly with 

 large lateral process. Antennae reaching process on 

 first abdominal segment. eiseni. 



6 (5). Terminal spines of inner ramus not nearly half as long 



as ramus. Second segment of outer ramus with a spine. 

 Inner ramus extending slightly beyond middle of first 

 segment of outer ramus. Third segment of outer 

 ramus hairy and about twice as long as the inner, which 

 is smooth. First abdominal segment longer than re- 

 mainder of abdomen, armed laterally with strong spines. 

 Antennae extending beyond tips of f ureal setae. 



albuquerquensis. 



7 (3,4). Inner ramus 1-segmented. 



8 (9). Terminal spines of inner ramus smooth, more than 



half as long as ramus, which is rounded at apex and 

 hairy. Second segment of outer ramus straight, as 

 long as or longer than preceding segment ; armed at 

 base of third segment with short spine, shorter than 

 either of the two on third segment. Inner spine of 

 third segment hairy, about twice as long as the outer, 

 which is smooth. Both spines considerably longer 

 than the segment itself. Last thoracic segment armed 

 on each side w T jth two small spines. First abdominal 

 segment shorter than remainder of abdomen, dilated, 

 armed with large spines ; second segment very short. 



