No. 39] ODONATA OF CONNECTICUT: COENAGRIONIDAE 57 



2. Tracheae of gills in alga-like patches (PI. i, Figs. 8 and 9) j- g^j^uj^ 



Tracheae of gills not in alga-like patches 3 



3. Lateral keels of the first abdominal segment with o to 2 spines ; 



axes of the gills clear .• • • • 4 



Lateral keels of the first abdominal segment with 2 to 4 spines ; 

 axes of the gills more or less clouded carunculatum 



4. Dorsal marginal spines of the median gill usually less than 20 in 



full-grown nymphs ; all of the third antennal segment dark 

 brown; gills rarely more than 4.5 mm. in length (PI. i, Fig. 7) 



geminatum' 

 Dorsal marginal spines of the median gill more than 20 in full- 

 grown nymphs ; only the proximal third of the third antennal 

 segment dark brown ; gills 5.5 to 6 mm. in length 5 



5. Marginal spines of both lateral and median gills not reaching the 



middle of the gill civile 



Marginal spines of both lateral and median gills reaching much 

 beyond the middle 6 



6. Tracheae of the gills numerous (PI. i, Fig. 11) durum 



Tracheae few (PI. i, Fig. 12) doubledayi 



7. Tracheal branches of the gills in alga-like patches ; caudo-lateral 



margins of the head behind the eyes greater than half the distance 



between the antennae 8 



Tracheal branches of the gills not in alga-like patches ; caudo- 

 lateral margins of the head behind the eyes less than half the 

 distance between the antennae 9 



8. Dark portion of the base of the gills less than half their length 



(PI. II, Fig. 4) traviatum 



Dark portion of the base of the gills extending more than half 

 the length of the gill (PI. 11, Fig. 9) exsulans 



9. Spines of the lateral abdominal keels not grouped conspicuously 



near the caudal ends of the keels on each segment ; gills as in 



P-.Ftex' : } '"""Xe"" 



Spines of the lateral abdominal keels grouped conspicuously near 

 the caudal ends of the keels on each segment; gills as in PL 11, 



Figs. 5, 10 10 



10. Median gill with a bunch of heavy spines on the dorsal margin 

 proximad of the first transverse cross-band; distal cross-bands 

 of about the same degree of blackness as the proximal ones ; 

 median gills not expanded greatly distad of the first cross-band 

 (PI. II, Fig. 5) signatum 



Median gills without a bunch of spines on the dorsal margin proxi- 

 mad of the first transverse cross-band, sometimes with a few 

 weak, well-distributed spines ; distal cross-bands much lighter 

 in color than the proximal ones, and sometimes wanting ; median 

 gill usually well expanded distad of the first transverse cross- 

 band (PI. II, Fig. 10) vesperum 



Adults, Males 



I. Three cross-veins in both wings between M* and Cui between the 



subnodus and the quadrangle durum 



Two cross-veins in both wings between Mi and Cui between the 

 subnodus and the quadrangle 2 



^ An exuviae, possibly minusculum, received from Dr. Calvert differs from geminatutn 

 in having no spines on the keels of segments i to ?.. This was referred by Dr. Calvert 

 to vesperum but is doubtfully that species. (Trans. Am. Ent. Soc. xlv, 384-385; 1919.) 



