542 



Enallagma exsulans (Hagen) 



Nymph. — Color, dark lirown or greenish. 



Head slightly hroader tlian long, the caudo-lateral angles pro- 

 jecting caudad and provided with heavy setae; second antennal seg- 

 ment shorter than the first, the lirst two darker than the remaining 

 ones and pilose; lal)ium extending just caudad of the procoxae, mental 

 setae three in nunil)er: lateral setae four or five, and six or seven 

 marginal setae on tlie median lobe. 



Thorax : legs with a few hair-like setae, the femora each with a 

 preapical ring of brown and the tibiae with the usual scales at the tip; 

 apices of the third tarsal segments and the apices of the claws dark; 

 nietathoracic wing-cases extending caudad to the fourth al)dominal 

 segment. 



Abdomen slender, the cuticle provided with minute setae and 

 minute brown spots ; lateral keels well developed on segments i-8, 

 the keels on segments 4—8 and the lateral apex of segment nine with 

 small groups of two to five setae; gills (Figs. 53, 77, 77a) I)roadl}' 

 lanceolate, broadest beyond the middle, usually heavily pigmented on 

 the proximal two-thirds, the area of infuscation being followed by 

 two large clear spots on each side of the axis, the distal end of the 

 gill being dark, the extreme tip white; marginal setae of the median 

 gill consisting of a dorsal row extending from the base to the light 

 spots, or nearly two-thirds the length of the gills, and ventral marginal 

 setae of the lateral gills of similar extent; apical margins of all gills 

 hairy ; smaller tracheae forming alga-like patches ; ovipositor extend- 

 ing to the middle of the tenth abdominal segment. 



Measurements 



Length 12-13.5 mm. 



TjpnRth of abdomen 9-10 mm. 



Lonfith of gills 5.5-7 mm. 



Width of gills 1.8-2 mm. 



TiOiisth of median lobe 2 mm. 



Width of median lnl)c 6-1.8 mm. 



Adult; Male. — Color, pale i)lue, black, and brown. 



Head pale blue and black ; median lobe of the labium bufif, sulv 

 triangular, the cleft oI)tuse at the base; antennae entirely black; post- 

 dypeus Ijlack, shining, tlie anteclypeus pale and the labrum with a 

 transverse black stripe on the dorsal margin; exposed portions of the 

 mandibles, their trochantins. genae, atid a transverse area between 



