DASTPOGONI.VAB 



ROBBER FLIES OF THE "WORLD 



123 



terminalia not rotate. Base of wing in males often 

 whitish. The flies range from quite small to large in 

 size in most species. Length in most species about 25 

 mm. Length 11 to 35 mm. 



Head, lateral aspect: The head is long. The eye is 

 narrowed below. The face for a short distance beneath 

 the antenna is usually nearly plane with the eye. The 

 face on the lower portion is quite prominent and gener- 

 ally arises abruptly from the flat, short portion above; 

 cheeks prominent. The occiput is thick throughout, 

 with abundant, coarse pile below; weak bristles begin 

 near the middle of the head and form a sublateral band 

 of several rows, becoming quite numerous above. Post- 

 vertex on either side with a patch of 7 or 8 stout bristles. 

 The proboscis is stout, tapered at the apex on the ventral 

 part, extended well beyond the face, and with a promi- 

 nent carina. Palpus of two segments ; the first is hemi- 

 cylindrical and excavated, the second short, quite robust, 

 often curved, with an apical pore, and bristly pile. The 

 antenna is attached near the upper third of the head, 

 approximately as long as the head and usually slender. 

 The first segment is a little longer than the second, both 

 with stout, short, ventral bristles. The third segment, 

 excluding microsegment, is 1*4 to rarely twice the 

 length of the first two segments combined ; third rarely 

 wider than the second segment at any point; it is usu- 

 ally gently and slightly attenuate, occasionally with 

 an angular dilation near the middle in species which ap- 

 proach Ospriocerus Loew. Third segment with two 

 microsegments, the first of them short, but distinct, the 

 second long, of variable length, attenuate, and spine- 

 tipped. 



Head, anterior aspect: Face pubescent, the cheeks 

 often largely or wholly bare. Flat upper portion of 

 face generally with a few short, weak bristles or bristly 

 pile. Middle of the face on the lower gibbous portion 

 with a large triangle of numerous, long, stout bristles 

 and occasionally some bristly hairs. Head about as 

 wide as high, nearly circular; the face is narrow at the 

 antenna, ranging from one-tenth to one-seventh or one- 

 sixth the head width, and strongly divergent below. 

 Front rather long, slightly divergent along the eye 

 margins, with a row of stout bristles and some bristly 

 pile. The front is pollinose and shallowly sunk in the 

 middle, sometimes with additional, submedial pile. 

 Vertex scarcely excavated at all, the ocellarium large, 

 but comparatively low with on either side 2 to 5 pairs 

 of bristles and 3 to 7 pairs behind. Anterior eye facets 

 only a little enlarged. 



Thorax: The mesonotum is comparatively high, 

 steeply sloping behind, still more anteriorly. It is 

 thickly covered widely over the whole surface with 

 subappressed, short, bristly pile ; acrostical bristles not 

 differentiated ; dorsocentral bristles differentiated only 

 on the posterior half, where there may be from 4 to 8 

 rows, or there may be a broad band of several irregular 

 rows of rather stout bristles for the whole medial third ; 

 this band may continue at reduced length to the anterior 

 margin. The lateral complement of bristles includes: 

 3 to 7 stout humeral, 1 to 10 posthumeral, 2 to 6 noto- 



pleural, 2 to 7 supraalar, 2 to 7 suprapostalar, 2 to 12 

 postalar, 3 to 5 scutellar pairs. Metanotal callosity 

 micropubescent only ; scutellum usually micropubescent 

 only, thick, rather convex, with an occasional scattered 

 hair. Pronotal collar with stout bristles. Lateral 

 pronotum usually with numerous, stout bristles, some- 

 times with only stiff pile. Lateral propleuron densely 

 pilose; prosternum dissociated; mesopleuron only 

 with micropubescence except in rare instances where 

 posteroventrally there are a few hairs. Upper sterno- 

 pleuron with a characteristic patch of numerous, fine, 

 or stiff pile, sometimes reduced in the small species to 

 3 or 4 fine wisps of pile. Metapleuron never with pile 

 or bristles; lateral metasternum likewise without pile 

 or bristles. Postmetacoxal area membranous. 



Legs: The femora are stout, only the anterior and 

 middle pairs being slightly or moderately swollen 

 toward the base. Pile on both femora and tibiae dense, 

 appressed, rather shoi-t and setate. Bristles are ex- 

 ceptionally numerous, stout, but relatively short 

 throughout. On the hind femur are 7 lateral, in the 

 smaller species 4, and 10 ventrolateral bristles, or as few 

 as 5 ; the apex ventrolaterally has a transverse cluster 

 of 3 to 5. In small species bristles are scarcely more 

 than setae; these have the medioapical bristles of 2 

 stout elements ; the larger species have 5 stout elements, 

 1 prominent dorsomedial bristle at the subapex. Hind 

 tibia with 2 to 6 dorsomedial, 3 to 7 dorsolateral bris- 

 tles, and a like number of ventrolateral bristles. Mid- 

 dle femur with 4 or 5 anteroventral, 5 to 10 ventral 

 bristles, at least 1 stout posterior bristle on the outer 

 fifth, and 2 to 4 stout anterior bristles. Anterior femur 

 with 2 to 4 posterior bristles; 7 to 10 ventral bristles 

 often doubled or trebled by additional rows. On the 

 middle and anterior tibia the smaller species have 4 

 bristles in each of the principal rows and 2 in the ven- 

 tral row, whereas the larger species have at least 5 and 

 usually 6 or 7 bristles in these rows. Protibial apex 

 without spine, all apical bristles removed from the 

 apex. Tarsi end in stout, sharp claws, well developed 

 pul villi, and a bladelike empodium. 



Wings: The wings are elongate, generally tinged 

 with brown or yellow to a slight but varying degree. 

 Marginal cell open, slightly narrowed ; anterior branch 

 of third vein ends above the wing apex, posterior branch 

 a somewhat greater distance behind. In the type of 

 genus and many other species the first posterior cell 

 is widely open, at most a little narrowed, but in a few 

 species it may be even closed and petiolate. In Sfeno- 

 pogon heteroneurus it has a long stalk and in addition 

 the second posterior cell is divided into 2 parts by an 

 extra crossvein. The fourth posterior cell is usually 

 closed and stalked, sometimes closed in the margin, or 

 even open. Anal cell open or narrowly closed. Alula 

 large; ambient vein complete. 



Abdomen : The abdomen is broad at the base but not 

 quite as wide as the mesonotum; it is rather strongly 

 tapered and elongate. The sides are generally curled 

 and quite convex, the whole subcylindrical. The pile 

 is abundant but short, appressed and setate, becoming 



