529 



two, three, and four. In mature nymphs there is an indefinite, dark 

 dorsal stripe extending from near the apex of the third segment to the 

 seventh or eighth; gills (Fig. 70) transparent, lanceolate, with a broad, 

 usually pale, opaque stripe along the axis from the base to near the tip; 

 dorsal marginal setae of the median gills usually more than twenty in 

 number and extending one-third the length of the gill from the base, 

 the ventral setae of the same gill consisting of only a few setae and 

 extending half as far as the dorsal row; ventral marginal setae of the 

 lateral gills of similar extent to the dorsal setae of the median gill; 

 apical margins usually without setae or hairs ; ovipositor of the female 

 extending to the middle of the tenth abdominal segment and the lateral 

 valves with about four heavy setae on the ventral margin. 



Bleasw'ements 



Length 13.5-14 mm. 



Length of abdomen 8-9 mm. 



Length of gills 5.5-6 mm. 



Width of gills 1.2 mm. 



Length of metathoraeic wing-eases. .3.6 mm. 



Length of median lobe 2.5 mm. 



Width of median lobe 5-2 mm. 



Adult; Male. — Color, dark blue or buff and black. 



Head blue or buff and black, the labium buff, the median lobe 

 subtriangular, the palpus moderately narrow ; antennae entirely black, 

 the first segment paler at the apex; postclypeus with a large, shining 

 black spot, the ventro-lateral margins pale ; anteclypeus, and labrum 

 except a dorso-mesal black spot and a dorso-lateral spot on each side, 

 pale ; exposed portions of the mandibles, their trochantins, the genae, 

 and a transverse stripe above the clypeus, pale; remainder of the front 

 and vertex dull black ; postocular spots oval, buff or blue, and not 

 usually connected with the stripe caudad of the ocellar area; occiput 

 and postgenal regions pale except a black stripe caudo-ventrad of the 

 postocular spots. 



Thorax blue or buff and black, the pronotum dull black with a 

 transverse median stripe on the cephalic lobe, the caudal margin of 

 the caudal lobe and small crescentic spots on the lateral margins of the 

 median lobe buff or blue ; dorsal third of the proepimera black, the 

 ' dorsal suture indistinct, the remainder of the sclerite buff or blue ; ceph- 

 alo-lateral angles of the mesostigmal plates elevated, the elevated por- 

 tion pale ; pale stripe of the mesosupraepisternum regular, the margins 

 parallel and straight, the stripe extending from the cephalic margin 



