Odonata — Plecioptera. 43 



in either wing, media and cubitus much reduced and usually indistinct. 



(Oligotoma.) OLIGOTOMID^ 



Cerci strongly asymmetrical, first joint of left cercus variously deformed, usually 

 dentate within; neuration usually complete. (Anlsembia) (PI. 8, fig. 173). 



EMBIID^ 



\ ORDER ODONATA. 



(LIBELLULOIDEA, PARANEUROPTERA.) 



Slender predatory insects, usually of large size and usually 

 strong fliers; head mobile, eyes large, three ocelli; antennae minute, 

 mouth inferior, mandibles strong; pro thorax small but free, 

 meso- and metathorax fused, abdomen long and flexible, cerci one- 

 jointed; legs not large, similar, placed far forward, tarsi three- 

 jointed; wings four, nearly alike; elongate, membranous, 

 net-veined, not folded, with characteristic nodus, arculus and tri- 

 angle and with the radial sector crossing the anterior branch of the 

 media. Metamorphosis considerable, the nymphs aquatic, no rest- 

 ing pupal stage. 



1. Wings alike, held on edge over the abdomen in repose; eyes stalked. Damsel 



flies. (ZYGOPTERA.) 2 



Wings somewhat dissimilar, horizontally out-spread in repose; eyes not ped- 

 uncled. Dragon flies. (ANISOPTERA.) 3 



2. At least five antecubital crossveins between the first and second veins before 



the nodus. (Calopteryx, Hetaerina) CALOPTERYGIDjE 



Only two antecubital crossveins. (Lestes, Enallagma) (CfENAGRI- 

 ONID.E) AGRIONIDiE 



3. Antecubital crossveins of first and second series not meeting except at base of 



wing. (Anax, iEschna, Gomphus, Cordulegaster) (Including GOMVHWiE 



CORDULEGASTRIDM ^SCHNID^ 



Antecubital crossveins of first series meeting those of the second. (Libellula, 

 Diplax, Cordulia) (PI. 8, figs. 176, 178) (Including CORDULIID.E) 



USELLtUDM 



\J ORDER PLECTOPTERA. 

 (EPHEMEROPTERA, EPHEMEROIDEA, AGNATHA, EPHEMERIDA.) 

 Delicate insects with short antennae and rudimentary mouth. 

 Hind wings generally present and much smaller than the forewings. 

 Two or three long caudal filaments present. Nymphs aquatic, 

 gill-bearing, suddenly changing to the adult. Adults short lived, 

 but molting before sexual maturity. May flies or Sand-flies. 



(Hexagenia, Baetis, Heptagenia) (PI. 8, figs. 181, 183) EPHEMERIDiE 



