AMERICAN DIPTERA. 333 



appear as single-jointed. The third joint is very large and gener- 

 ally sherical or oval in form, although in some genera (Conicera, 

 Hypocera and Melaloncha, etc.) it may be elongated and drawn out 

 into a point. The arista is composed of two short basal joints and 

 a Ion-', usually more or less plumose third joint; its insertion may 

 he either dorsal or terminal. The palpi are nearly always large 

 and elavate, with a scries of strong bristles along their outer margin. 

 In the males of some species the palpi are much enlarged, or they 

 may be destitute of the characteristic bristles. The proboscis is 

 usually of moderate size and soft consistency; in some forms, how- 

 ever, it is very strongly chitinized, and in a few others it is greatly 

 elongated or swollen. 



The thorax is well developed in the winged forms, and is often 

 considerably arched above, so as to partly conceal the head; again, 

 in the wingless females of some genera it is exceedingly small and 

 often shorter than the head. The dorsum usually bears macrochaetse 

 along the sides, medially behind and on the scutellum. The meta- 

 thorax is very short. 



The legs are large and strong and well adapted to jumping. The 

 anterior coxa? are much elongated and more or less freely movable 

 at the base. The four posterior ones are connate with the thorax. 

 The femora, especially the hind ones, are often exceedingly stout 

 and flattened. The tibiae of all the legs may bear either rows of 

 setulaa or large, strong, single, paired or serial macrochset?e on the 

 outer side before the apex. Often part of the tibiae and metatarsi 

 are covered with close comb-like rows of flattened bristly hairs. 

 These are very characteristic of the Phorida?. Tibial spurs and 

 tarsal claws are usually present, although the former may rarely be 

 absent. The empodia and pulvilli are nearly always present, but 

 are wanting in a few of the genera. Peculiar modifications of the 

 legs are rare, and when they do occur apply only to the tarsi and 

 femora. The femora may be extremely flattened, and the tarsi may 

 be flattened or swollen. The wings are present in the males of all 

 o-enera so far as is at present known, but are absent or very much 

 reduced in size in the females of quite a large number of the genera. 

 Their unique venation when present serves at' once to distinguish 

 them from any other known Diptera. 



The wings are large and are folded flat on the back when 

 not in use. The costa is thickened along its basal half to form 



TRANS. AM. ENT. SOC. XXIX. OCTOBER. 1903 



