2o6 CONNECTICUT GEOL. AND NAT. HIST. SURVEY [Bull. 



Tribe Eucorduliini Tilly ard 



Nymphs without frontal horns ; tip of abdomen consisting of 

 long segments, except the tenth, which is short. Adults have the 

 triangle of the hind wing not distad of the arculus, the proximal 

 side about on a line with the latter. 



Key to Genera 

 Nymphs 



1. Lateral spines of segment 9 as long as, or longer than the termi- 



nals ; teeth of palpi or lateral lobes as long as wide (except in 



Tetragon euria ) 2 



Lateral spines of segment 9 not reaching the ends of the terminals ; 

 teeth of palpi or lateral lobes much shorter than wide 4 



2. Lateral spines of segment 8 set at an angle to the long axis of the 



abdomen (PI. iv, Fig. 6), not parallel to those of segment 9 ... 



Neurocordulia 

 Lateral spines of segment 8 not set at an angle, and parallel to 

 those of segment 9 3 



3. Lateral setae four or five; length, full grown 27 mm. . . . Epicordulia 

 Lateral setae seven; length, full grown about 16 mm. . .Tetragoneuria 



4. Dorsal spines or prominences absent Cordulia; Somatochlora 



Dorsal spines or prominences present, the elevations hook-like in 



some genera 5 



5. Dorsal spines or hooks present on segments 3 or 4 ....Somatochlora 

 Dorsal spines or hooks absent on 3 and 4 6 



6. Dorsal hooks or prominences on 6-9 inclusive, those on 7-9 long, 



hook-like ; lateral spines on 9 reaching the tips of the terminal 



appendages Helocordulia 



Dorsal hooks or prominences on 5 to 8 or 9, those on 7-9 not long 

 or hook-like; lateral spines on 9 not reaching the tips of the 

 terminal appendages Dorocordulia 



Adults 



1. Front wings with the area between M4 and Cui enlarged at the 



distal end so that the rows of cells are greatly increased towards 



the margin of the wing ( PL x, Fig. 4) 2 



Front wings with the area between M4 and Cui not enlarged at the 

 distal end so that the rows of cells are greatly increased towards 

 the margin, but of nearly equal width throughout 3 



2. Triangle with cross-veins (PL x, Fig. 4) Neurocordulia 



Triangle without cross-veins (PL xvi, Fig. i) Wilhamsonia 



3. Two cubito-anal cross-veins present In the hind wings ; antenodals 



never infuscated (PL xiv, Fig. 4) Somatochlora 



Only a single cubito-anal cross-vein in the hind wings; or if with 

 two, then some of the antenodals infuscated 4 



4. Triangles of the front wings without cross-veins (PI. x, Fig. 3) 



Dorocordulia 

 Triangles of the front wings with cross-veins 5 



5. Wings without black basal marks (PL xi, Fig. 2) Cordulia 



Either front or hind wings with black basal marks 6 



6. Triangles of the hind wings with cross-veins ; wings with black 



spots at nodus and tip (PL xiv, Fig. 2) Epicordulia 



Triangles of the hind wings without cross-veins ; wings without 

 black spots at nodus and tip 7 



