545 



the tips; metathoracic wing-cases extending to the caudal margin of 

 the fourth abdominal segment. 



Abdomen with moderately well-developed lateral keels on seg- 

 ments one to eight inclusive, the first without setae, the second with a 

 bunch of three or four, the third with an irregular double row, and 

 the fourth to the eighth possessing irregular single rows, with some- 

 times two setae at the apices; segment nine, although possessing no 

 keel, has an irregular double row of setae in line with the keels of the 

 preceding segments; gills spatulate to lanceolate (Fig. 72), without 

 pigment except in the smaller tracheae and sometimes a trace along 

 tlie axis; dorsal marginal row of setae of the median gill extending 

 much less than half the length of the gill and containing seventeen or 

 eighteen setae, the ventral row of the same gill short and composed of 

 only a few setae ; ventral marginal row of the lateral gills also less than 

 one-half the length of the gills; the black tracheae of the gills differ 

 greatly from those of other clear-gilled species in being fewer in num- 

 ber and branching from the axis more nearly at right angles ; oviposi- 

 tor extending caudad to the apex of the tenth abdominal segment. 



Measurements \ 



Length 11-12 mm. > 



Length of abdomen 9 mm. ' 



Length of gills 4,7 mm. 



Width of gills 1.3 mm. 



Length of metathoracic wing-cases ... 2 mm. 



Length of median lobe 2 mm. 



Width of median lobe 6-1.5 mm. 



Adult; Male. — Color, pale blue (pale methyl-blue), black, and 

 buff. 



Head blue and black, the mouth-parts buff, with a tinge of blue; 

 median lobe of the labium subtriangular, the cleft shallow and rounded 

 at the proximal end; labial palpi with slender distal segments, pale, 

 and not darker at the tip ; antennae dark brown or black, the tips of the 

 first and second segments sometimes pale; postclypeus shining black 

 except the latero-ventral angles, which are blue; anteclypeus and 

 labrum except a small dorso-mesal black spot, blue ; exposed portions 

 of the mandibles, their trochantins, genae, and a transverse area dorsad 

 of the clypeus blue; remainder of the front black; postocular spots 

 large, blue, rather irregular and frequently serrate on the margins; 

 pale stripe caudad of the ocelli wanting; occiput and postgenae buff, 



