20 



Fresh-water Biology 



{Continued from page 18) 



50 — Gills widest in middle, one third as broad as long Amphiarion 



— Gills widest toward the distal end, one sixth as broad as long Chromagrion 



51 — Mental setae of labium 1 or 2 Nehalennia 



— Mental setae 3 to 7 52 



52 — Gills ending in slender tail-like tips 53 



— Gill tips blunt or merely acute 58 



53 — Gills with about 6 crossbars of brown Zonlagrion 



— Gills with fewer crossbars or with none 54 



54 — Length of body 18 mm Teleallagma 



— Length of body 11 or 12 Ischnura 



55 — Notch in upper margin of middle gill beyond its middle 56 



• — This notch before middle of gill or wanting 57 



57 — Width of gill more than a third of its length Telebasis 



— Width of gill less than a third of its length Coenagrion 



58 — Gill tips rounded Hesperagrion 



— Gill tips angulate or slightly pointed 59 



59 — Gills not pigmented: slender Anomalagrion 



— Gills more or less strongly pigmented Enallagma 



KEY TO THE GENERA OF AQUATIC HEMIPTERA 



(After Hungerford; Kansas Univ. Sci. Bull., Vol. 11, 1919.) 



1 — Antennae shorter than head 2 



— Antennae as long as or longer than head, exposed 6 



2 — Hind tarsi with indistinct setiform claws (save in Plea which is less than 3 mm. 



long) 3 



— Hind tarsi with distinct claws 4 



3 — Head overlapping thorax dorsally. Front tarsi 1 -segmented, palaeform Corixidae 



(1 genus) Corixa 



— Head inserted in thorax. Front tarsi normal — Notonectidae 10 



4 — Membrane of hemelytra (front wings) reticulately veined 5 



— Membrane of hemelytra without veins — Naucoridae 12 



5 — Apical appendages of the abdomen long and slender; tarsi 1-segmented — Nepid.\e.13 

 — Apical appendages of the abdomen short and flat, retractile — Belostomatidae . . 14 



6 — Head as long as entire thorax; both elongated. Both about 10 mm. Hydrometridae 



(1 genus) Hydrometra 



— Head shorter than thorax including scutellum 7 



{Continued on page 22) 



PLATE 7. DAMSELFLY NYMPHS 



Genera 



Agrion 



Amphiagrion. 

 Anomalagrion 

 Archilestes. . . 



Argia 



Coenagrion . . 

 Chromagrion. 

 Enallagma. . . 

 Hesperagrion. 



Figs. Length Distr. Water L.Set* M 



1 20 



7 11 

 10(6) 8 



4(3) 30 



2 12-17 

 (8) 13 



5(7) 12 



8 12-15 

 (8) IS 



G 

 G 



E, S static 

 C, W static 



G 



N 



E 



G 



SW 



lotic 

 static 5-6 

 5 

 3 



1-4 

 6-7 



5 



4-5 



6 



both 



static 



static 



both 



static 







4 



4 



7 





 4-6 

 3-4 

 2-4 

 3-4 



Genera Figs. Length Distr. Water L.Set* M 



Hetaerina. . . 12(1) 18 E,S,W lotic 







Hyponeura. . (2) 22 



Ischnura. ... 6 11-13 



Lestes 3 20 



Nehallennia.. 9(6) 11 



Telagrion . . . . (6) 18 



Telebasis. ... (6) 14 



Zonagrion. . . (8) 14 



SW 

 G 

 G 

 G 



SE 

 SW 

 SW 



lotic 0-1 

 static 5-6 



static 

 static 

 static 



static 6-7 

 static 5 





 

 4 

 5 

 1 

 3 

 2 

 3 



* Raptorial setas inside the labium; L, lateral; M, mental setas. 



