ROBBER FLIES OF THE WORLD 



501 



virtually absent. The second submarginal cell of the 

 wing is long and slender, the middle and hind femora 

 and their tibiae are distinctly lengthened and the su- 

 perior forceps of the male generally is long and slender. 

 Slender, small to medium size flies. Length 12 to 

 20 mm. 



Head, lateral aspect : The head is of moderate length, 

 the face plane with the eye or even simken below it on 

 its upper half. On the lower half of the face is a low 

 elevation with a slightly beaked appearance; the vvhole 

 face is nearly plane in profile. The occiput is extremely 

 short, barely visible in profile with a low, slight swell- 

 ing dorsally behind the vertex. The pile of the occiput 

 is scanty and fine ventrally with fine, slender, down- 

 turned bristles and bristly hairs in the middle and 3 to 

 6 pairs of slender bristles behind the upper eye corner 

 which may be of contrasting color. Proboscis slender, 

 longer than the face, with the basal third a little swollen 

 and almost no dorsal keel. The apex is bluntly rounded 

 with minute hairs above and somewhat longer hairs 

 below. Palpus small, slender, cylindrical, with 1 or 2 

 weak, apical bristles and some bristly hairs. The an- 

 tenna is attached at the upper fifth of the head and is 

 unusually elongate. The first two segments are com- 

 paratively short; the first segment is nearly twice as 

 long as the second, and has several, appressed bristles 

 at the apex extending around to the dorsal surface. The 

 third segment is very long and slender, as wide or 

 sometimes less wide than the second segment and more 

 than twice as long as the first 2 segments combined. At 

 its apex it bears a short microsegment followed by a 

 slightly longer, thick style as wide as the microsegment, 

 which carries a minute, apical bristle. 



Head, anterior aspect: Tlie head is as wide as the 

 thorax and only a little wider than high; cheeks of 

 moderate extent. Face below antenna quite narrow, 

 less than a tenth the head width and moderately di- 

 vergent below. The surface, including the cheeks and 

 the large oblique subepistoma, is pubescent. Pile is 

 absent on the upper half ; on the low ventral elevation 

 are a very few, fine, short hairs and near the middle of 

 each half a vertical row of 3 long, slender bristles. 

 Along the epistomal margin is a transverse row of 2 to 

 4 pairs and an additional pair placed just above the 

 epistomal group. Front small, pollinose with an ocular 

 row of 2 or 3 fine hairs. The vertex is scarcely exca- 

 vated anteriorly but rather deeply behind. The ocel- 

 larium is conspicuous and large with vertical sides and 

 bears a single pair of slender hairs behind the ocelli. 



Thorax : The mesonotmn is comparatively high, con- 

 vexly arched, more steeply arched anteriorly and pos- 

 teriorly ; it is pollinose and bears a very few, fine, scat- 

 tered, suberect setae with a differentiated, double acros- 

 tical row and with short dorsocentral elements differen- 

 tiated anteriorly, becoming progressively longer to- 

 wards the scutellum. Humerus pilose ventrally and 

 the lateral complement of long, comparatively stout 

 bristles contains 2 notopleural, sometimes 1 posthu- 

 meral, 1 postsupraalar, 1 suprapostalar, 2 postalar, and 

 1 pair of scutellar bristles. Scutellum not very thick 



but convex, with distinctly impressed rim. Pronotum 

 with only fine pile, generally, but sometimes with 1 pair 

 of bristles. Postmesopleuron with a few, scattered, fine 

 hairs and a few posteriorly on the pteropleuron, 1 or 2 

 on the sternopleuron, and 4 or 5 on the posthypopleuron. 

 Metapleuron with 7 or 8 long, slender, fine bristles. 

 Metanotal callosity pollinose only. Metastemum 

 pilose; presternum fused with the propleuron and with 

 a seam between. 



Legs : All the femora are slender, the middle and 

 hind pairs together with their tibiae and tarsi are dis- 

 tinctly elongate; the pile is fine, subappressed and 

 setate, and there is no ventral fringe of pile except for 

 a short, scanty row on the ventral surface of the an- 

 terior tibia and a still more scattered row ventromedial- 

 ly on the hind femur. Bristles are moderately abimdant 

 but, with a few exceptions, are quite short, sharp but 

 slender; the hind fenmr bears 1 lateral bristle on the 

 basal fourth, 4 ventrolateral, 2 still longer ventral on 

 the basal fourth ; at the subapex dorsally is a striking 

 bristle on each side, but none at the apex. The hind 

 tibia bears 3 or 4 dorsolateral including a prominent, 

 basal element and 1 dorsomedial beyond the middle be- 

 sides a single, well developed ventrolateral bristle on 

 the apical fifth; apex with 6 bristles. Middle femur 

 with 2 conspicuous, anterior bristles, 3 or 4 anteroven- 

 tral bristles and on the base 1 or 2 long, ventral bristles. 

 In some species the ventral bristles are 5 in number and 

 shorter. Middle tibia with a single, dorsal bristle near 

 the middle, 2 conspicuous ventral bristles on the outer 

 half and 1 distal, posteroventral bristle. Anterior 

 femur with only a short bristle on the anterior surface 

 near base and apex; in some species with 2 posterior 

 bristles along the middle and generally with 2 ventral 

 bristles near the base. The anterior tibia bears 1 dorsal 

 bristle and 2 exceptionally prominent, long, postero- 

 ventral bristles and a ventral row of bristly hairs. An- 

 terior basitarsus as long as the next 3 segments, the 

 middle and hind basitarsi longer than the next tlixee. 

 Claws slender and sharp, the pulvilli and empodium 

 well developed. Trochanters with 2 or 3 medial bristles. 



Wings : The marginal cell is closed and stalked and 

 in freakish individuals closed at the apex. The sub- 

 costal cell and anterior border of the marginal and 

 submarginal cells villose. The second submarginal cell 

 is exceptionally narrow, arising in an arch from the 

 plane base of the third vein. The anterior branch ends 

 at the apex, posterior branch behind. Fourth posterior 

 cell closed and stalked, the anal cell likewise. Alula 

 moderately large, the ambient vein complete. 



Abdomen: The abdomen is rather slender and sub- 

 cylindrical, never as wide as the mesonotiun. The pile 

 is scanty, subappressed setate, with a few, longer hairs 

 along the sides of the first four tergites. Sides of the 

 first tergite with 6 or 7 pairs of slender bristles and the 

 lateral subposterior margins of all the remaining ter- 

 gites with conspicuous slender bristles. Males with 

 eiglit tergites, the last being half as long as the seventh 

 and well developed. Females with seven tergites, the 

 ovipositor beginning beyond this. Male terminalia 



