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UNITED STATES NATIONAL MUSEUM BULLETIN 224 



The wings have all the cells open and often clouded on 

 the crossveins. The apical protibial spine is very 

 slender and strongly curved. In the males these flies 

 are readily recognized by the wide, apically flared and 

 completely flattened, terminal portion of the abdomen, 

 which usually shows a silvery, shining, micropubescent 

 sheen. Eelated to the Cophura Osten Sacken group of 

 genera. Length 9 to 13 mm. 



* Head, lateral aspect : The face is scarcely visible in 

 profile and becomes only slightly produced on the lower 

 half. The eyes are short, equally developed above and 

 below, convex anteriorly, slightly convex behind. The 

 occiput is moderately developed throughout except at 

 the immediate vertex, where it is set off from the eye 

 by a crease. Pile of occiput scanty above, abundant, 

 long and fine below, with 12 to 14 pairs of moderately 

 stout bristles on the upper half. Those behind the 

 vertex are longer and stouter. The proboscis is short, 

 obtusely rounded apically, strongly compressed later- 

 ally and with a high, conspicuous medial ridge. The 

 apex has a few, fine hairs, the base below has a few 

 long, stiff hairs and the outer, dorsal margin of the 

 proboscis on either side of the medial ridge, bears 5 or 

 6 short, stout bristles. Palpus with the first segment 

 excavated, second microporate and with a number of 

 bristly hairs below but none at apex. The antenna is 

 attached at the middle of the head; the first two seg- 

 ments are quite short and beadlike, of equal length. 

 The third segment is long and slender, slightly nar- 

 rowed at the immediate base and tapered at the imme- 

 diate apex; it bears two microsegments, the first quite 

 short, the second long, attenuate with apical spine; pile 

 of the first two segments long and stiff, with 1 to 2 stout, 

 moderately long bristles ventrally on each segment. 

 The front is quite steep and almost vertical, deeply 

 excavated, the ocellarium unusually large with nearly 

 vertical sides, large anterior ocellus, placed low and 

 bearing 2 to 3 pairs of weak short or more rarely long 

 stout bristles in the middle area, besides 1 slightly 

 longer, stouter pair immediately behind the ocelli, an- 

 other on the posterior slope. Eye facets strongly 

 enlarged. 



Head, anterior aspect: The face below antenna is 

 about a fourth of the head width, and divergent below. 

 Subepistomal area small, nearly horizontal. The face 

 is coarsely pubescent with 2 or 3 rows of weak, long 

 bristles above the epistoma and with some long, fine 

 pile on the upper portion of the face. 



Thorax : the thorax is pollinose, the pile of the mes- 

 onotum is scanty but rather long, the acrostical row is 

 single and well differentiated, the dorsocentral ele- 

 ments become quite long, though never very stout and 

 begin in front of the suture. Humerus with long pile ; 

 in the type of genus the following complement of stout, 

 lateral bristles is present : 3 notopleural, 2 or 3 supra- 

 alar, 2 postalar, and 2 to 5 pairs upon the scutellum, 

 these usually more slender. Propleuron with abun- 

 dant, long, fine pile only, including the upper posterior 

 portion. Anterior sternopleuron with a few hairs, 

 metapleuron with 10 or 12 long, slender, bristly hairs; 



remaining pleuron apilose; lateral metanotal slopes 

 micropubescent only. Lateral and ventral metaster- 

 mum with abundant, long, fine pile ; the latter is broad, 

 isolated, chitinized; the postmetacoxal area is large 

 and membranous; tegula pubescent only. Presternum 

 dissociated. 



Legs: All the legs are comparatively slender; the 

 hind femur is very slightly dilated distally and dis- 

 tinctly though moderately bent near the apex, espe- 

 cially in the male. The hind tibia is quite slender at the 

 base, gradually and strongly swollen apically until at 

 the apex 2 or 3 times as wide as the base. First two 

 or three segments of the hind tarsus are swollen in the 

 males, less so in the females. In the type of genus 

 there is this complement of bristles: The hind femur 

 without distinct bristles but 2 long, slender, bristly 

 hairs dorsoapically and medially at the apex, and on 

 the basal half ventrally 3 or 4 rather long, slender, 

 erect, bristly hairs or weak bristles ; the ventral pile is 

 scanty, short and erect, the dorsal pile fine, long and flat 

 appressed. The third tibia bears 6 or 7 dorsal bristles, 

 the basal ones short, 2 lateral bristles at the middle and 

 beyond, 2 longer, stouter, ventral bristles on the outer 

 third. Middle femur with numerous, long, fine, bristly 

 hairs ventrally in 2 rows besides several elements an- 

 teriorly. The midtibia bear conspicuous, quite long, 

 oblique, basally stout, attenuate bristles consisting of 

 3 anterodorsal, 3 ventral with the longest ventral ele- 

 ments basal, and also there are 5 or 6 shorter posterior 

 and 3 or 4 short dorsal bristles. Anterior femur with 

 long, fine, ventral pile ; its tibia has 2 dorsal and 3 quite 

 long, basally stout posterior bristles; the apex has a 

 small, strongly curved, pointed spine without basi- 

 tarsal modification. All tarsi end in sharp claws, long 

 pulvilli and slender empodium. 



Wings : The marginal cell and all the posterior and 

 the anal cell widely open. Middle vein at the end of 

 the second basal cell long; anterior cross vein beyond 

 the middle of the discal cell. Alula moderately large; 

 ambient vein complete. 



Abdomen: At the base, the abdomen is as wide as 

 the mesonotum; it is a little narrowed at the base 

 of the second segment, then slightly widened to the 

 end of the third segment. Pile of the abdomen scanty, 

 short, setate and appressed, a little longer on the sides 

 especially on the first 2 tergites. First tergite laterally 

 with 3 or 4 long, slender bristles. In the male 6 tergites 

 present ; at the end of the second tergite the abdomen 

 begins to widen, and on the fourth to the sixth it is 

 quite flat and flared into a shovellike plate which com- 

 pletely covers the remaining tergites and the rather 

 small terminalia. In the last 2 tergites, in males the 

 fifth and sixth, are densely silvery pollinose or ap- 

 pressed micropubescent when viewed from the front. 

 Female with 8 tergites, the eighth a third to half as 

 long as the seventh, which is a little shorter than the 

 sixth. Male terminalia rotate one-fourth to the left, 

 rather small and inconspicuous. It is dominated by 

 the epandrium which is cleft and slightly divergent 

 from the base, with the enclosed proctiger extending 



