89 
Abdomen very elongate, acuminate toward the end, 
scarcely depressed; segments slightly increasing in length 
posteriorly to the Sth; 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. 
