551 



rows together; ovipositor extending to the middle of the tenth ab- 

 dominal segment, the ventral margins of the lateral valves with a 

 si.'.gle row of setae ; venter of the abdomen without the median black 

 stripe of signatitui, but with a double row of black spots near the 

 apical margins, two on each of segments one to six and sometimes 

 on seven also; gills (Fig. 57) lanceolate, frequently much and suddenly 

 widened beyond the middle, conspicuously banded, usually with two 

 darker cross-bands (more or less fused) near the proximal third 

 and three lighter crescentic ones which are sometimes wanting, axis 

 dark, the median gill without dorsal marginal setae, the ventral margins 

 of the lateral gills with a thick row extending slightly more than 

 one-third the length of the gills from their bases, or extending from 

 the base to the point where the first dark cross-band reaches the margin. 



Mcasuremenis 



Length 15.5 mm. 



Length of abdomen 9 mm. 



Length of gills 5.5 mm. 



Length of metathoracic wing-eases. . .4.1 mm. 



Length of median lobe 1.8 mm. 



Width of median lobe 5-1.5 mm. 



Adult; Male. — Color, lemon-yellow (strontian yellow) or very 

 pale blue, and black; the majority of specimens are yellow, the blue 

 tenerals being infrequent. 



Head yellow and black ; labium pale yellow, median lobe subtri- 

 angular; antennae brown and pale, the first segment and basal two- 

 thirds of the second pale, the remainder dark brown ; postclypeus 

 with a large black spot occupying almost the whole of it and within 

 which are two small yellow spots ; anteclypeus and labrum yellow 

 except a median, dorsal, brown spot on the labrum ; exposed portions 

 of the mandibles, trochantins, genae, and a transverse area above 

 the clypeus extending dorsad to the level of the median ocellus, yellow ; 

 remainder of the front black except a small transverse stripe 

 cephalad of the median ocellus and small spots cephalo-ventrad of 

 the lateral ocelli ; postocular spots large, cuneiform, connected with 

 the narrow stripe caudad of the ocellar area ; the black of the vertex 

 extends along the margin of the compound eyes a short distance 

 caudad and ventrad of the postocular spots and sends mesad a broad, 

 short band ; remainder of the occiput and postgenae pale yellow. 



Thorax yellow and black ; pronotum yellow and black, the broad 

 cephalic lobe mostly yellow, the median lobes each with a large yellow 



