Moiionraph o/ Égyptian Diplera. 29 



1, DACUS Fabricius. 

 F., Syst. Antl., 21Ô. (ISUÔ); Mek;.. Syst. Beschr., VI. 22.1. (1S30). 



Easily distiiigui.slied froin ail tlie other gênera by its weak and 

 incomplète chaetotaxy, the long stigma and by the inferior angle of 

 Cu cell, which is extremely elongated and pointed. 



Head broader than high; frons fairly broad; face somewhat 

 swollen in the middle, but flattenedand with well developed anten- 

 nal furrows reaching the epistoma;eyes rather small and fairly pro- 

 minent ; occiput usually without any latéral swellings : cheeks usually 

 narrow; proboscis very short, not geniculate; palpi small; antennae 

 inserted at, or immediately below the middle of the eyes, narrow 

 and very elongated on account of the third joint, which is about 

 two and a half times the length of the second; arista bare; cephalic 

 chaetotaxy incomplète and weak; oc. and pvt. absent; vt. not strong; 

 ^•.0/'. 1, i.or.2, ail weak; ocp. aosent; genal bristle almost obsolète. 



Thorax characterised by its very weak chaetotaxy ; the humerai 

 callus is always very prominent, conspicuous and lighter in colour; 

 usually the praealar callus (bearing the posterior îipl.) is aiso pro- 

 minent and paler in colour; .sr^^.l or 2; de, prsc. and st. absent; 

 ,>/>!. 2: a.s(r absent; p. sa. 2; mpi.l; pt. more or less strong; scutellum 

 with a pair of u.sc. only. Abdomen usually fairly elongated, dis- 

 tuictly narrowed at the base, convex and entirely devoid of bristles 

 or bristly hairs; the five abdominal segments are often fixed and 

 fused together: maie hypopygium small; female ovipositor shows 

 considérable variation in length in différent species; it is usually 

 cylindrical, but it may be quite short and cylindrical or fiât; or it 

 may be as long or even longer than the abdomen, in which case it is 

 cylindrical and its length is due to the basai joint ; legs normal ; mid- 

 dle tibiae with a single spur. Wings normal in shape without any 

 conspicuous bands or spots, and characterised by the inferior angle 

 of Cu cell which is extremely elongated, sometimes reaching almost 

 to the hind margin of the wing; stigma narrow and very elongated; 

 costal bristle absent; costal vein thickened ; Se. indistinct; RI bristly, 

 ending before, at, or after the radio-median cross-vein; R2 + 3 not 

 straight, near Ri ; R4 + 5 bristly over its whole length, usually much 

 bent and diverging from Ml ; Ml curved after the médian cross-vein; 

 M3 + Cul much diverging from Ml; Cu2 + 2ndA long, reaching the 

 hind margin ; radio-median cross-vein always placed after the middle 



