66 



year; in the case of G. ri/losipcs, of two years. The iiiiagos 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. 

 [GoNiphui^ Needh.) 

 (id. Dorsal hooks represented more or less on 2 or 3 to 9. 

 bb. Dorsal hooks distinct, each produced at the hinder niar- 

 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. (jmslinellus. 



b. Dorsal hooks fee1)ly 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. 



