No. 39] ODONATA OF CONNECTICUT: COENAGRIONIDAE 37 



4. Gills with tracheal branches much more numerous at the widest 



portion of the gill ; abdomen with small white spots on a dark 



background Nehallenia, p. 49 



Gills with tracheal branches equally distributed throughout the 

 length of the gill ; abdomen with brown spots on a light back- 

 ground 5 



5. Gills with blunt points, or if with long points, then the cuticular 



pigment other than in cross bands ; mental setae usually three, 

 or three with a minute fourth (four in E. cah'crti and E. 



cyaihigeriini) Enallagma, p. 54 



Gills with long tapering points ; the cuticular pigment, if present, 

 always in cross bands ; mental setae of the labium usually four 6 



6. Gills without cuticular pigment; no dark spots at bases of abdom- 



inal spines ; nymphs of small size, full-grown individuals rarely 

 more than 14 mm. in length including gills (PI. 11, Fig. 7) 



Anomalagrion, p. 38 

 Gills usually with cuticular pigment in the form of arcuate cross 

 bands ; cuticular spots present and prominent on abdomen and 

 keels ; nymphs larger, when full grown 16.5-20 mm. in length 

 including gills Ischnura, p. 40 



Adults 



1. Cephalic row of setae of middle and hind tibiae twice as long as 



the intervals between their bases ; postnodal cross-veins of the 

 front wing twelve or more in number ; M2 arising between cross- 

 vein 5 and 9 in the front wing Argia, p. 85 



Cephalic row of setae of middle and hind tibiae less than twice as 

 long as the intervals between their bases ; postnodal cross-veins 

 of the front wings usually less than twelve in number;" M2 

 arising between the third and fifth, rarely sixth postnodal cross- 

 veins in the front wing 2 



2. Dorsum of thorax metallic green or bronze Nehallenia, p. 49 



Dorsum of thorax not metallic green or bronze 3 



3. Postocular spots wanting ; mesopleural suture without a black 



stripe • 4 



Postocular spots present ; mesopleural suture with a black or dark 

 brown stripe 5 



4. Dorsum of abdominal terga 1-6 entirely reddish or buff; female 



with a heavy spine on caudal margin of the eighth sternmn 



Amphiagrion, p. 48 

 Dorsum of abdominal terga 1-6 black ; female without a heavy 



spine on the caudal margin of the eighth sternum 



Chromagrion, p. 46 



5. Mo usually arising between the fourth and sixth postnodal cross- 



veins in the front wings and between the third and sixth in the 



hind (Fig. 9, No. 3) 7 



M2 usually arising between the third and fourth postnodal cross- 

 veins in the front wings and between the second and third in 

 the hind 6 



6. Dorsum of the fourth abdominal tergum black, except a narrow 



basal ring; stigma of the front wing of the male not remote 



from the margin (Fig. 9, No. 7) Ischnura, p. 40 



Dorsum of the fourth abdominal tergum yellow with the exception 

 of a basal and apical spot in the male and a small apical spot in 

 the female ; stigma of the front wing of the male remote from 

 the margin (Fig. 9, No. 8) Anomalagrion, p. 38 



^ More than 12 in Chromagrion and occasionally in Enallagma. 



