DIPTERA BRACHYCERA 



TROMOPTERA 



Two pad-like pulvilli only. Strong bristly hairs or even 

 bristles usual on the thorax, and spicules or even bristles on 

 the legs, with an apical circlet of spines on the tibi?e. Aerial 

 flies, usually clothed with dense furry pile. 



Head usually holoptic, but sometimes dichoptic in the male, and 

 without cephalic bristles (except a pair of ocellar bristles in Toxo2Jhora) ; 

 never sunk between the eyes on the vertex in such a way as to make 

 the eyes appear protuberant ; collar never bristly. Eyes always bare, 

 facets all equal in size in both sexes (Conf. Systrojnis), and (as far 

 as is known) unicolorous and not brilliantly colored in life. Antennse 

 with the third joint never annulated, and usually with a style or arista or 

 pencil of hairs which when present is always terminal. 



Thorax either with or without bristles, eromochsetous though densely 

 pubescent in most Bomhylida:, Ijut closely allied species may have 

 praesutural bristles or strong bristly hairs on the postalar calli, and in 

 many genera numerous strong bristly bairs may occur on other parts 

 until in the ToxopJiorince and the Therevidcc strong chtetotactic bristles are 

 present (figs. 294, 311), though no bristles ever occur on the pleura3. Strong 

 tufts of dense pubescence are almost always present on the mesopleura3 and 

 metapleurse, but the hypopleur?e are bare in order to allow free move- 

 ment of the middle femora. Scutellum unarmed, but often with a few 

 strong marginal bristles. 



Abdomen ordinarily without any approach to bristles amongst the 

 furry pubescence, though strong hairs may occur. Genitalia rarely at 

 all conspicuous, but the ovipositor is sometimes {Anthrax, Therevd) 

 provided with a circlet of spines as in some Mydaidce and Asilidm. 



Legs usually weak and thin, only adapted for alighting ; femora 

 often with bristle-like spicules on the underside, which become strong in 

 some species, tibite with minute spicules and an incomplete apical 

 circlet of spines in the Bomhylidcc, which develop into rows of bristles and 

 a complete apical circlet of spines in the Toxo-phorincc and Tlicrcvidcc. 

 Pulvilli never more than two, and even these sometimes obsolete {Anthrax, 

 etc.). 



Wings with a venation of the ordinary type for the earlier families of the 

 Brachycera, but in the Bomhylida; the posterior cells are never more than 

 four in number and the small cross-vein is always absolutely absent, while 

 in the Thercvidce the posterior cells are always five in number and the 



470 



