76 NORTH AMERICAN DIPTERA. 



27. DOLICHOPODID^E. 



BY PROF. J. M. ALDRICH. 



Small flies, never exceeding 7 mm. in length, almost always 

 green in ground color, usually shining, more rarely dusted 

 with gray or brown, sometimes pure yellow or almost black. 

 As a family they are distinguished from their nearest allies 

 by the absence of the cross-vein between the discal and second 

 basal cells, these uniting to form a single cell. 



Head about as wide as the thorax (much wider only in 

 Psilopinae), usually a little wider than high ; the face bare, 

 very wide to very narrow, or the eyes contiguous below the 

 antennae ; front generally widening rapidly above (in Dia- 

 phorus the eyes sometimes contiguous above), with bristles 

 on the vertex only. Posterior orbit with a well defined row 

 of short, erect bristles (toward the mouth indistinct in Hydro- 

 phorinse and some other genera); proboscis fleshy, short, 

 retracted, rarely a little protruding ; antennae three-jointed, 

 inserted more or less above the middle of the eyes, the first 

 two joints never much elongated, the third commonly oval, 

 but in several genera lengthened ; arista dorsal, subapical, or 

 completely apical. Thorax higher and longer than wide, with 

 regularly arranged bristles on the dorsum ; in some genera a 

 well-marked flattened or concave area before the scutellum. 

 Abdomen tapering, conical or a little compressed (in Hydro- 

 phorus and Scellus sometimes peculiarly small and retracted), 

 without noticeable bristles in most genera ; the male hypopy- 

 gium usually prominent, varying greatly in form, and in the 

 degree in which it is concealed in the abdomen. Coxee gen- 

 erally short, legs in most genera of medium length, sometimes 

 elongated, those of the male frequently developed into some 

 ornamental structure ; the front femora are thickened in a few 

 genera. Wings usually hyaline, yet often with dark mark- 

 ings, which may take the form of a definite pattern, or may 

 follow the veins indistinctly, or may be evenly diffused ; in 



