200 A. L. MELANDER. 



absent, one or two submarginal cells, and two to four posterior cells 

 may be present, the anal cell present or wanting ; if present closed 

 far from the border of the Aving (except in the Mythicomyinse which 

 properly do not come within the limits of this family). The front 

 border of the wing is provided with small bristles, which in at least 

 one species takes on the character of curved hooks. The formation 

 of the anal angle is of generic distinction, it may be rectangularly 

 developed or diminished to an even curve. Tegulse small, simple, 

 not conspicuously ciliated, halteres simple. 



Little is known of the metamorphoses of the Empidse. The larvae 

 are said to resemble those of the Asilidse. They have been found in 

 rich earth, under leaves and other decaying vegetable matter. The 

 pupae are free, and with two porrect points at the anterior end. 



The Empididse are all predaceous flies, though at times they are 

 found about flowers. Many of the species fly in swarms in an serial 

 dance over brooks or shrubbery. Some of the smaller forms fly 

 close to the ground and alight on stones. All are rather sluggish in 

 movement and therefore easy to catch. 



As an example of the habits of these flies we may cite Hilara 

 trivitatta, the most conspicuous of the early spring insects of central 

 Texas, and the only one that appears in numbers at that time of the 

 year. 



Coming before the Bibios and taking the place of the later-appear- 

 ing Ephydridae the flies swarm in immense numbei's over the swiftly- 

 running streams. Over open pools, especially where the water moves 

 swiftly, the flies skim along the surface, almost all oriented alike, 

 facing windward. By a gradual zig-zag flight they reach the wind- 

 ward edge of the pool, when some, hovering a moment, are blown 

 back, while the others take a sharp turn and fly to the starting 

 point. A part fly with the feet touching the surface of the water, 

 others skim along a few inches higher. In the sunshine a swarm of 

 the flies can be seen hovering and zig-zagging at a height of several 

 feet above the brook. 



When copulating the pair float on the surface, and are swiftly 

 carried down stream. The more curious of the skimming flies come 

 one by one to settle on the drifting pair, and then fly away to some 

 other object. If a bit of grass be sent down stream the flies come 

 one at a time in quick succession to it, impelled either by hunger or 

 by the feeling of assisting a helpless object. This latter point is 



