ORDER DIPTERA. 129 



often prolonged to a point. Front on each side with two rows of 

 bristles, one of which is situated more above and in front, the other 

 below and exteriorly. Border of the inouth with no vibrissae. 

 Clypeus none or rudimentary. Proboscis never thickened. Only 

 the middle tibia; with spurs; all the tibiae without an erect bristle 

 on the outer side before the tip. Ovipositor horny, consisting of 

 three elongated retractile segments like the drawers of a telescope, 

 the last of which ends in a simple point. Trypeta florescetitm Linn. 

 Europe and North America. 



Family Ortalidse. Venation of the wings complete; auxiliary vein 

 separated from the first longitudinal vein, and running to the border 

 of the wing in the usual way, under an acute angle, and remaining 

 perfectly distinct in its whole length; third longitudinal vein gen- 

 erally with coarse hairs; two posterior basal cells large, and the out- 

 ward one frequently prolonged in an acute angle. Front with 

 bristles on the upper part only; no vibrissae at the border of the 

 mouth; clypeus commonly very much developed, and proboscis 

 often very much thickened. Middle tibiae alone with spurs; no 

 tibiae with an erect bristle on the exterior side before the tip. 

 Ovipositor of the female rather flattened and horny, consisting of 

 three elongated segments, forming three drawers like those of a 

 telescope, and ending in a simple point. Pyrgota undata Wied., 

 Tritoxuflexa Wied. 



FIG. 151. Tritoxa flexa, onion fly, and maggot. 



Family Micropezidse. Body long and slender; legs short; front 

 with bristles near the crown. Calobata antennipennis Say. 



Family Psilidae. Body slender; face receding, mouth small. 

 Psila bicolor Meig. Europe and North America. 



Family Sciomyzidae. Front with two bristles, one behind the 

 other, on the side before the vertical bristles; middle tibiae with a 

 greater number of bristles at the tip. Sciomyza, albocostata Fallen. 

 Europe and North America. 



Family Helomyzidae. Front bristly on the upper half only; all the 

 tibiae spurred. Ilelomyza, apicalis Loew. 



Family Cordyluridae. Venation of the wings complete; both pos- 

 terior basal cells of considerable size; auxiliary vein well separated 

 from the first longitudinal vein, which is bare. Entire side of the 



