49 



evidently watching for game, and making short dashes forward 

 betimes, presumably to seize some small insect driven from 

 shelter by the wind. 



Mr. Adams and Mr. Hart observed a large swarm which 

 gathered in the lee of the field laboratory boat August 8, at 

 twilight, and after half an hour or more of rapid circling about 

 scattered abruptly at about 7:40. An adult A}iax was once 

 seen to devour an agrionid imago. 



The species covers the continent from Alaska to the West 

 Indies, and is found in eastern Asia. 



Cabot ('81, p. 15; PL I., Fig. 2) has figured the nymph, and 

 many different reproductions of his figure are current. The 

 following brief description covers the more important char- 

 acters. 



The nymph measures 45 mm.; abdomen, 31 mm.; hind 

 femur, 8 mm.; width of abdomen 8 mm., of head 8 mm. 



The head is flat and broad, widest across the posterior 

 third of the eyes. Antennae minute, slender. Eyes broad, lat- 

 erally prominent, produced well toward the dorsal median line 

 at their posterior internal angles. Labium very long and flat, 

 extending posteriorly beyond bases of middle legs; median lobe 

 with a narrow median cleft. Lateral lobes oblong, denticulate 

 along inner margin, an incurved tooth at tip; hook long, strong. 

 Abdomen widest across segment 7, tapering both ways. No 

 trace of dorsal hooks; short lateral spines on segments 7 to 9. 

 Hind margin of 9 (as seen from above) straight. Superior 

 appendage a trifle longer than segments 9 and 10, notched at 

 tip; inferior appendages a little longer, sharp pointed; lateral 

 appendages half as long. 



Young nymphs are more unlike full-grown ones in habitus 

 than are those of most other species. In the earlier stages the 

 abdomen appears more attenuated toward the base. The supe- 

 rior appendage is at first very short and blunt and directed 

 upward, but after a few molts it becomes elongated and 

 notched at the tip, though it remains for a time much shorter 

 than the inferiors. Lateral spines on 7 to 9 appear very early. 



