508 



tlic tenth nhdominal se.s,nnent and setose on the ventral margin; apical 

 mars;in of the tentli alwlominal tergum cleft nearly to the hase, the 

 margin thickly heset with short spines; gills (Fig. 58) uniform dark 

 gray or nearly lilack. paler at the tip, long, broad, and bluntly pointed, 

 the margins parallel for a considerable distance. 



Mcasurtnicnts (i/ouiui nijmphs) 



Length 14 mm. 



Length of abdomen 9 mm. 



Length of gills 5-6 mm. 



"Width of gills 3 mm. 



Length of metrithoraeie wing-eases ... 4 mm. 



Length of median lobe 3.5 mm. 



Width of median lol)e L5-3 mm. 



Descriljed from a male specimen in tiie collection of the Illinois 

 State Laboratory of Natural History taken from the Kankrd<ee River 

 si.K miles below Kankakee. June i, 1901, and se\eral specimens ob- 

 tained from Dr. E. M. Walker. 



Adult: Male. — Color, black and cinnamon-buff. 



Head : uiedian loI)e of the laliium 1)uff. sul)triangular ; di.stal seg- 

 ment of the palpus dark at the tip; antennae IjJack, first two segments 

 nearly equal, the first pale at the apex, the third segment longest; clyp- 

 eus and lal)runi buff, the postclypeus with two indefinite black spots 

 near the f ronto-clypeal suture ; lalirum with a mesal spot on the dorsal 

 margin; front and genac l)utT, tiie pale color extending dorsad to the 

 ocelli, the black confined to an indefinite ring around the median ocellus 

 and wedge-shaped marks on the vertex: occiput black: the surface 

 of the head dorsad of the postclypeus and the occiput often becomes 

 pollinose and obscures the original coloration. 



Thorax : prothorax dark brown or black, more or less pollinose 

 with age; caudal lobe of the pronotum black, median lobes each with 

 a large, ]);de, circular, median spot wl.ich often becomes pollinose be- 

 fore the rest of the notum : proepinieron pale, the noto-ejiimeral suture 

 indistinct though marked by a lilack stripe: dorsal carina black and 

 a black stripe on each side one-half tiie width of the mesepisterna: 

 mesopleura! suture lined witii black ; mese])imera with a broad sooty 

 line extending the entire length of the sclerite and more than half as 

 wide; metapleural suture lined with black, the metepisterna and mete- 

 pimera and the postcoxal areas usually buf?; legs rather short, striped, 

 the dorsum of all femora witli a broad stripe including tlie cephalo- 

 ventral row of setae: tarsi and claws black; wings clear, the stigma 



