66 | 
year; in the case of G. villosipes, of two years. The imagos are 
all much alike, of medium size, with clear wings, the triangles 
normally without cross-veins, the thorax with green or yel- 
lowish stripes. They disappear rapidly after transformation, 
and are not usually common. 
KEY TO THE KNOWN NORTH AMERICAN NYMPHS OF GOMPHUS. 
AAA. Four pairs of lateral spines; lateral labial lobes rather 
finely toothed, with 6 to 12 teeth; side margin of 9 
spinulose or denticulate, 10 (last) wider than long. 
(Gomphus Needh. ) 
aa. Dorsal hooks represented more or less on 2 or 3 to 9. 
bb. Dorsal hooks distinct, each produced at the hinder mar- 
gin of its segment in a pointed median tooth; side 
margins of 9 spinulose. 
cc. Lateral spines of 9 about as long as segment 10; 9 
thrice as long as 10. 1. sp. (a). 
c. Lateral spines of 9 reaching about half way to the api- 
cal angles of 10; 9 twice as long as 10. 
2. graslinellus. 
b. Dorsal hooks feebly elevated, only the last two or three 
forming median teeth in the hind margin of the 
segment ; side margins of 9 obsoletely denticulate. 
3. descriptus: 
a. Dorsal hooks represented only by median teeth in the pos- 
terior margin of 8 and 9; a fine smooth median line on 
the preceding segments; 9 spinulose laterally, 10 very 
short. 
dd. Lateral spines of 9 distinctly shorter than the distance 
to the median tooth of the segment; labial apical 
hook sharp, projecting beyond the teeth. 
ee. Lateral spines of 9 broad, scarcely longer than those of 
8; length of ventral surface of 9 at middle a little 
more than one third its basal width; abdomen less 
than twice as long as broad. 5. abbreviatus. 
