52 



ing from a few days to a few weeks according to species. Dur- 

 ing this season they are little in evidence. Indeed one may not 

 see a living adult, although thousands of fresh exuviae be 

 scattered along the banks. 



The structural characters of the nymph appear early, and 

 the descriptions which follow will apply to all but the very 

 youngest nymphs. The structures latest to develop are per- 

 haps the teeth on the inner margin of the lateral labial lobes, 

 which in some species, at least, increase in number with succes- 

 sive molts. On account of the short life and restricted range 

 of flight of the imagos they are not often taken in ordinary col- 

 lecting. If the shores, boats, and bridges near the larval 

 haunts are examined early each day in the latter part of June 

 and early in July, the collector may be rewarded some morn- 

 ing by finding large numbers in the act of emerging ; and if 

 these are kept alive and uninjured in a roomy box or cage their 

 colors and texture will mature in a few days. 



KEY TO THE GENERA OF ADULT GOMPHID^ OF THE EASTERN 



UNITED STATES. 



aa. Both triangles with a cross-vein. II. Progomphus. 



a. Both triangles without a cross-vein, except the discoidal tri- 

 angle in Hagenius. 

 hh. First and second anal veins distinctly angulated toward 

 each other at the cross-vein of the anal loop, which 

 contains 3 to 5 cells. 

 cc. Discoidal triangle of usual shape, without cross-vein ; 

 3d femora not reaching base of 2 ; anal loop 3-celled. 



IV. Diastatomma. 



c. Discoidal triangle distinctly 4-sided, with cross-vein ; 

 3d femora very long, reaching base of 3; anal loop 

 with 3 to 5 cells, usually 4. V. Hagenius. 



h. First and second anal veins nearly parallel, or only the 

 first angulated ; anal loop with 1 or 2 cells. 

 dd. Part of arculus of hind wing above attachment of sec- 

 tors much shorter than that below them, the lower 

 sector joining it at or above its middle; length of 

 body 40 mm. or less. VI. Lanthus. 



