89 



Abdomen very elongate, acuminate toward the end, 

 scarcely depressed; segments slightly increasing in length 

 posteriorly to the 8th ; 9 about twice as long as 8, its sides 

 nearly parallel on apical half ; 10 very short; smooth mid-dorsal 

 line on 2 to 7, a flattened rudiment of a dorsal hook on apex of 

 9 ; short lateral spines on 6 to 9, those of 9 about half as long 

 as the superior appendage ; appendages subequal. 



Young nymphs in the station collection, dredged from the 

 bed of the creek, some not more than one third grown, show 

 these same characters very clearly marked. 



