16 



Fresh-water Biology 



{Continued from page 14) 



17 — Lateral spines on abdominal segments 7-9 Anax 



— Lateral spines on abdominal segments 6-9 Aeschna 



— Lateral spines on abdominal segments 4 or 5-9 18 



18 — Low dorsal hooks on segments 7-9 Nasiaeschna 



— No dorsal hooks on abdomen Epiaeschna 



20 — Inner edge of lateral lobe of labium coarsely and irregu- 

 larly toothed (PI. 3a) Cordulegaster 



— Same, evenly and regularly toothed or entire 21 



21 — Head with a high frontal horn 22 



— Head smooth or with a low rounded prominence 24 



22 — Dorsal abdominal hooks sharp, flat and cultriform. . . .23 

 — Dorsal abdominal hooks thick and blunt . Neurocordulia 



23 — Head widest across the eyes Macromia 



— Head widest across the bulging hind angles . . . Didymops 



24 — Dorsal hook on the ninth abdominal segment 25 



— No dorsal hook on the ninth abdominal segment 29 



25 — Lateral setae of labium 5 26 



— Lateral setae of labium 7 27 



B 



26- 



-Lateral spines of 9 surpassing tips of terminal appendages 



Epicordulia 



-Same shorter not surpassing tips of terminal appendages 

 Perithemis 



-Lateral spines of 9 surpassing tips of terminal appendages 

 Tetragoneuria 



-Same, shorter not surpassing tips of terminal append- 

 ages 28 



-Length under 15 mm Helocordulia 



-Length over 20 mm Somatochlora 



-Eyes at sides of head 30 



-Eyes capping anterolateral angles of head; more frontal 

 than lateral 40 



30 — Abdominal appendages strongly decurved: lateral spines wanting Mesothemis 



— Abdominal appendages straight or but a very little declined; lateral spines on 8 and 9.31 



31 — Dorsal hooks present 32 



— Dorsal hooks absent 34 



32 — Spines of segment 9 very long Celithemis 



— Spines of segment 9 short or moderate 33 



{Continued on page 18) 



Fig. 1. Diagrams explana- 

 tory of terms used in the dra- 

 gonfly key. ^ is a labium (of __ 

 Perithemis); ml\s its median ^'~ 

 lobe; / /, its lateral lobe; m s, 

 mental setae; / s, lateral setae; 

 h, hook. 



B (Perithemis) and C 

 (Anax) are from end of ab- _„ 

 domen as viewed from above; ^o- 

 8, 9, 10 are the three last seg- 

 ments; d, h, dorsal hooks; / sp, 

 lateral spines; /, lateral and s, 29- 

 superior, and i, inferior ap- 

 pendages. 



Genera 



Aeschna 1 



Anax 7*(1) 



Basiaeschna 4(3) 



Boyeria 3 



Coryphaeschna. . 2 



Epiaeschna 5 



Gynacantha. ... (1) 



PL.\TE 5. DRAGONFLY NYMPHS 



Figs. Length Distr. Waters 



Genera 



Figs. Length Distr. Waters 



Nasiaeschna .... 6 



Didymops 11 



Epicordulia 8 



Helocorulia 12 



Macromia 10(11) 



Neurocordulia... 9 



Tetragoneuria... (8) 



• A young nymph; the bands of color later disappear. 



The first 8 are Aeschninae, with flat labium. The remainder are Cordulinae with spoon-shaped labium. 

 The lateral spines of the abdomen are in No. 2 on segments 7-9; in 1, 5 and 7, on 6-9; in 4, 6 and 8, on 5-9; 

 and in No. 3, on 4-9. 



