14 



Fresh-water Biology 



KEY TO THE GENERA OF NYMPHS OF DRAGONFLIES AND 



DAMSELFLIES: ODONATA* 



1 — Gills within the stout spine-tipped abdomen (suborder Anisoptera: dragonflies) . . 2 



— Gills, three flat vertical plates at the end of the slender abdomen (suborder Zygop- 



tera: damselflies) 43 



2 — Labium flat 3 



— Labium spoon-shaped, covering the face up to the eyes 20 



3 — Antenna? short and thick 4 



— Antennae slender and bristle-like, Aeschninae 13 



4 — Antennae seven- join ted, Petalurinae . ^ Tachopteryx 



— Antennae four-jointed: third joint longest 5 



5 — Tenth abdominal segment as long as all other segments combined Aphylla 



— Tenth abdominal segment not longer than other single segments 6 



6 — Middle legs closer together at base than are the fore legs Progomphus 



— Middle legs not closer together at base than are the fore legs 7 



7 — Wing cases strongly divergent Ophiogomphus and Herpetogomphus 



• — Wing cases parallel 8 



8 — Abdomen and third antennal segment flat and nearly circular Hagenius 



— Abdomen and third antennal segment more elongate 9 



9 — Third antennal segment thin, flat, oval 10 



— Third antennal segment more nearly cylindric 11 



10 — Third antennal segment broadly oval Lanthus 



— Third antennal segment elongate Octogomphus 



11 — Dorsal hooks on abdominal segments 6-9 long and sharp 12 



— Dorsal hooks on abdominal segments 6-9 short and blunt Gomphus 



12 — Lateral abdominal appendages as long as inferiors Gomphoides 



— Lateral abdominal appendages shorter than inferiors Dromogomphus 



13 — Lateral lobes of labium armed with strong raptorial setas Gynacantha 



— Lateral lobes of labium lacking raptorial setae 14 



14 — Hind angle of head strongly angulate 15 



— Hind angle of head broadly rounded 17 



15 — Superior abdominal appendages as long as inferiors Coryphaeschna 



— Superior abdominal appendages much shorter than inferiors 16 



16 — Lateral lobe of labium squarely truncata on tip Boyeria 



— Lateral lobe of labium with taper pointed tip Basiaeschna 



* Since this key was prepared the nymphs have been described for a number of genera that are not included 

 in it, genera that occur only along the southern border of the United States. Two papers that will be especially 

 valuable for those who work in this region are: 



Insects of Puerto Rico and the Virgin Islands by Elsie Broughton Klots (NY. Acad, of Sciences, Scientific 

 Survey of Puerto Rico and the Virgin Islands, Part I, 107 pages, 7 plates). 



The Nymphs of North American Libelluline Dragonflies by J. G. Needham and Elizabeth Fisher (Transactions 

 of the American Entomological Society, 62: 107-116, 2 plates) 



A new genus, Tarnetrum, has been erected for the two species of Sympetrum (one of them, T. corruptum, 

 widely ranging) whose nymphs entirely lack dorsal hooks on the abdomen, and have the lateral spines of the 

 eighth abdominal segment very minute or entirely wanting. 



(Continued on page 1 6) 



PLATE 4. DRAGONFLY NYMPHS 



Genera Figs. Length Distr. Waters 



Aphylla 2 



Cordulegaster . . . 3 



D rom ogomphus . 7(5) 



Gomphus 5 



Gomphoides.... 6(5) 



Hagenius 9 



Genera 



Figs. Length Distr. Waters 



