68 
usually 2 or 3, broad and subtruncate, separated by 
deep narrow incisions; side margins of 9 entire, often 
fringed with soft hairs, as in AA, 10 not longer than wide. 
ii. Dorsal hooks very small, pointed on 6 to 9; lateral labial 
lobes 4-toothed. 14. exilis. 
i. Dorsal hooks wanting, except usually a distinct median 
tooth in the hind margin of 9; a fine smooth median 
abdominal line; labial lobes rarely more than 3-toothed. 
jj). length of ventral surface of 9 along median line not 
more than half its width at base. 
kk. Dorsal hooks entirely wanting; lateral spines of 9 
as long as segment 10. . 16. sp. (d). 
k. A broad triangular flat dorsal median tooth in the 
hind margin of 9, as long as segment 10; lateral 
spines of 9 twice as long as 10. 17. sp. (e). 
j. ‘Length of ventral surface of 9 more than half its width 
at base; apical hook of anterior tibiz very small. 
(Stylurus Needh. ) 
lll. Ventral surface of 9 distinctly shorter than its basal 
width; lateral spines of 9 about one third as long 
as their distance from the median dorsal tooth of 
the segment; median tooth minute. 18. amnicola. 
ll. Ventral surface of 9 about as long as its basal width; 
lateral spines of 9 at least two thirds as long as 
the distance to the median tooth. 19. plagiatus. 
l. Ventral surface of 9 twice as long as its basal width. 
21. spiniceps. 
1. Gomphus sp. (a). 
Gomphus sp., Hagen, '85, p. 264, No. 17 (nymph). 
This species is known only from a single nymph described 
by Dr. Hagen from Indiana. It may be distinguished by the 
following characters: 
Length 30 mm. Lateral lobes of labium with a sharp bent 
apical hook and ten strong teeth; median lobe straight; seg- 
ment 9 longer than 8, three times as long as 10; lateral spines 
