AET18 DIPTEKA OR TWO-WINGED FLIES ALDRICH 15 



rather fiat, only a few hairs above vibrissae; bucca very narrow, 

 hardly one-eighth the eye height. 



Mesonotum, except humeri, metallic blue-green, overlaid with 

 some white pollen, especially anteriorly; the two outer of the usual 

 dark stripes are rather distinct, the inner not so. Chaetotaxy: 

 dorsocentrals 2, 3 ; acrostichals 0, 1 ; humeral 2 ; posthumeral 1 ; 

 presutural 1; notopleural 2; supraalar 2 and a small behind; in- 

 trallar 2; postalar 2 (the front one small); scutellura with one 

 lateral, 1 apical, 1 discal; sternopleural 2, and a small hairlike one 

 below the posterior. Pleurae and humeri yellow. Calypters lightly 

 infuscated, the front one with black rim. Thoracic spiracles large, 

 yellow. 



Abdomen pale yellow at base, blue and violet at tip. The first 

 segment is yellow with a blackish narrow line at hind edge, extend- 

 ing below; the second segment is yellow with a purplish hind 

 border, wider at middle, where it is nearly half the segment and 

 very narrow below; third segment yellow anteriorly at side and 

 more below, the rest blue, but the hind border purple; fourth 

 segment blue above and below with a distinct white poUinose spot 

 each side of the genitalia and hardly a trace of purple apically. 

 The first segment has several lateral bristles, the second one, the 

 third a strong marginal row, the fourth a discal row of 8 and a 

 smaller marginal row. Genital segments of moderate size, brownish 

 or piceous, shining, with hairs but no bristles. Inner forceps yellow, 

 slender, nearly straight, with sharp black tips ; outer forceps yellow, 

 slender, strongly bowed in at tip. Fifth sternite small yellowish, 

 cleft in middle. 



Legs yelloAY, middle and hind tibiae and tips of their femora 

 black; hind tarsi lighter than their tibiae; middle tibia without 

 flexor bristle, hind tibia with long calcar a little below middle. 



Wings long and narrow, infuscated, more distinctly beyond tip 

 of auxiliary vein, but with no definite pattern; apical cell opening 

 on costa just before apex for a distance equal to one-seventh the 

 preceding costal segment. 



Female. — The front is narrowest at vertex, where it is 0.18 of the 

 head-width in both specimens ; cruciate bristles distinct, only 3 to 4 

 lower frontals of any size; orbitals represented only feebly by 

 hairs but the lower pair in one specimen a trifle stouter. Abdomen 

 with much less yellow, none above on the third segment, and a wider 

 dark margin on the second. 



Length of male, 8.5 to 9 mm. ; of female, the same. 



Described from three males and two females, La Suiza de Tur- 

 rialba, Costa Kica, February 23-28 and March 16, 1923 (Pablo 

 Schild). In Prof. P. L. Melander's collection. 



Paratypes.—M^ile and female, Cat. No. 26799, U.S.N.M. 



