53 
d. Parts of arculus of hind wing above and below attach- 
ment of sectors nearly equal, the lower sector join- 
ing it distinctly below the middle. 
ee. Hind femora long, reaching base of 3, with 5-7 long 
spines besides the usual spinules. 
VII. Dromogomphus. 
e. Hind femora usually moderate, with spinules but 
no long spines. VIII. Gomphus. 
KEY TO THE GENERA OF THE NORTH AMERICAN NYMPHS OF 
GOMPHID. 
AA, Tenth (last) abdominal very long and slender, many times 
longer than broad, nearly half the length of the abdo- 
men. I. Aphylla. 
A, Tenth abdominal usually broader than long, never more 
than twice as long as broad. 
aa. Middle legs approximated at base; inner pair of wing-cases 
strongly divergent; ventral longitudinal sutures of 
abdomen diverging to near apical angles of 8, segment 
9 similar to 10; lateral labial lobes entire, their apices 
rounded; 38d and 4th antennal joints subcylindric, 
more than twice as long as thick, the latter recurved; 
five or more pairs of lateral spines; dorsal hooks pres- 
ent but not prominent. Il. Progomphus. 
a. Middle legs at least as far apart as fore legs; ventral lon- 
gitudinal sutures of abdomen diverging to apical 
angles of 9, which is unlike 10; 4th antennal joint very 
short and small; not over 4 pairs of lateral spines, ex- 
cept in Hagenius. 
bb. Inner pair of wing-cases strongly divergent ; 3d anten- 
nal joint oblong, at least twice as long as broad ; lat- 
eral labial lobes dentate, without apical hook; tenth 
abdominal narrowing posteriorly, following the taper- 
ing outline of the apex of the abdomen. 
IW. Diastatomma, IV. Herpetogomphus. 
b. Inner pair of wing-cases parallel, lying close together 
