274 



UNITED STATES NATIONAL MUSEUM BULLETIN 224 



ventral bristles. Anterior femur similar and also with 

 a cluster of bristles dorsally and posteriorly near the 

 apex consisting of 5 dorsal bristles in a row and a 

 pair of posterior bristles. The tibia is similar, the 

 anterior bristles shorter but the posterior bristles 

 equally conspicuous. Anterior and middle tarsi also 

 with conspicuous, terminal circlet of 5 to 6 long bristles. 

 All tarsi end in long, slender, sharp, slightly curved 

 claws ; a long slender, basally thickened empodium ; the 

 pulvilli absent. 



Wings : The wings are hyaline ; marginal cell widely 

 open; anterior branch of third vein ends at the wing 

 apex. All posterior cells widely open; anal cell open; 

 alula moderately large; ambient vein complete; costa 

 with very sparse, coarse, long setae. 



Abdomen: The abdomen is comparatively short and 

 robust, basally as wide as the mesonotum, distinctly 

 shorter than the wings, the first tergite unswollen. 

 There are 6 tergites in the male, with the seventh show- 

 ing as a very narrow linear flap beneath the sixth; 

 sixth tergite without pollen, polished and bare ; remain- 

 ing tergites densely flat appressed, silvery pollinose. 

 There are eight tergites in the female, the last some- 

 what shorter, the last four without pollen. Pile of 

 abdomen restricted to a few, scattered setae and weak 

 bristles laterally. Sides of first tergite with moder- 

 ately abundant, curled, suberect, fine pile and with 5 

 stout, moderately long bristles in a row and closely 

 adjacent to one another. Sides of second tergite with 

 6 or more rather stout bristles; the third tergite with 

 only 3 or 4 very weak bristles or strong setae. Male 

 terminalia moderately large, of the ventrally open type, 

 partly rotate. Dorsal epandrium distinctly separated. 

 Gonopod short and robust basally with short dorsal 

 apical process. Proctiger cleft and but little longer 

 than the epandrium. Hypandrium extremely short 

 and undivided. Female acanthophorites each with a 

 row of 4 slender, sharp-pointed spines; no additional 

 spinous bristles below. 



Distribution; Nearctic: Omninablautus arenosus 

 Pritchard (1935). 



Genus Aterpogon Hardy 



Figuees 177, 188, 553, 557, 1124, 1133, 1742, 1983, 2033, 2115 



Aterpogon Hardy, Proc. Linnean Soc. New South Wales, vol. 

 55, p. 254, 1930. Type of genus : Aterpogon cyrtopogonoides 

 Hardy, 1930, by original designation. 



Small, hump-backed flies with dense, long, stiff, sub- 

 erect pile on the mesonotum. Both mesonotum and 

 abdomen are smooth and polished. The bristles are 

 greatly reduced. Probably related to Cophura Osten 

 Sacken, they differ in the unmodified epandrium, high 

 convex mesonotum with bristles restricted to very 

 weak, lateral elements and none on the scutellum. 

 Length 8 mm. 



Head, lateral aspect: The length of head is normal. 

 The face is almost completely plane and level with the 

 eyes, gently convex and receding below and very 



slightly visible in profile on the lower part. The eyes 

 are slightly recessive anteroventrally, leaving the oc- 

 ciput exposed below and obliterated on the entire upper 

 half, or at most barely visible. Pile of occiput sparse, 

 fine, moderately long and submarginal with the eye ; it 

 is a little more abundant on the lower third. Bristles 

 are absent, the upper pile being merely a little more 

 stiff. The proboscis is small, rather strongly com- 

 pressed laterally and from the upper view swollen a 

 short distance back from the apex and again near the 

 base; its lower apical surface is plane, the dorsal sur- 

 face gently rounded, the apex bluntly pointed with a 

 few fine hairs; base below with a few long hairs. Pal- 

 pus clearly of two segments, the first segment exca- 

 vated, the second segment porate ; both segments with 

 a few, long, stiff hairs below, the second with 2 or 3 

 hairs surrounding apex. The antenna is attached at 

 the upper third of the head, moderately long and slen- 

 der; the first segment is only half as long as the sec- 

 ond; the second considerably wider apically, and the 

 third not quite as wide as the apex of the second and 

 very slightly and gradually narrowed towards the 

 apex. Third segment bears an extremely short, mi- 

 nute, microsegment followed by a second, slightly 

 longer, apically tapered microsegment to wliich is at- 

 tached a minute, sharp, distinct spine. First segment 

 with a few, long, stiff hairs below and above; second 

 segment with a single, long, stout bristle apically; 

 entire upper margin with stiff, appressed setae. 



Head, anterior aspect: The face below antenna is 

 less than one-fourth the head width and divergent 

 below. Subepistomal area short, small, horizontal, 

 concave and bare. The face is micropubescent, with- 

 out pile on the upper half and with a patch of 8 stiff, 

 downturned hairs on either side below the middle, be- 

 sides a band of comparatively short, stiff bristles placed 

 in 2 or 3 rows transversely across the lower face. Sub- 

 epistomal margins with 2 or 3 stiff hairs. The front is 

 slightly divergent above the antenna, the vertex not 

 convergent. Sides of front with 4 or 5 stiff hairs on 

 either side; vertex moderately excavated; ocellar pro- 

 tuberance large, high, with vertical sides, the ocelli 

 large ; it bears 5 or 6 pairs of long, stiff, bristly hairs. 

 Eye facets strongly enlarged centrally. It will be noted 

 that from the anterior aspect the eyes extend down 

 below the face and below the lateral margin of the 

 posterior cheeks. 



Thorax: The mesonotum is rather strongly hump- 

 backed and convex both anteriorly and posteriorly, not 

 pollinose but with micropubescence narrowly on the 

 lateral mesonotal margin and over the whole pleuron. 

 The mesonotal pile is quite abundant, long and nearly 

 erect, and fine to stiff in quality without obscuring 

 the ground color; there is a double row of fine, not 

 bristly, acrostical elements followed by a narrow, bare 

 stripe. Humerus with long pile, lateral mesonotal 

 bristles reduced to 2 extremely weak, slender noto- 

 pleural elements; bristles absent beyond. There are 2 

 or 3 long, stiff hairs on the postalar region. The scu- 

 tellum has a fringe of 16 long, stiff hairs, and it is con- 



