INTRODUCTION. 9 



The first two of these characters will hardly ever mislead, if it is 

 borne in mind that they have no value in the genus Psilopus, 

 especially in the subdivision with black cilia on the tegulre. As 

 to the latter character (neuration) it should be remembered that 

 the peculiarities strikingly developed in the males as specific marks 

 are but slightly indicated in the female, and can be perceived only 

 by a very close observation. 



The habits of the Dolichopodidde are, as far as known, generally 

 predaceous. Most of them hunt for smaller diptera or other insects 

 with soft bodies, and suck them out. They are usually found in 

 damp places, covered with a rich vegetation ; many are principally 

 found on the leaves of aquatic plants, on stones, partly overflown 

 with water, on dams and near waterfalls ; some of them are able 

 to run rapidly over the water even when it is rippled by wind 

 {Hydrophorus) ; others are fond of salt or brackish waters 

 (Aphroxylus, Thinophilus and some Hydroplioi-us) ; the species 

 of Medeterus prefer dry situations and are found on stumps of 

 trees, fences, etc., even in very dry and hot weather. 



Little is as yet known about their mode of transformation. 

 Most species live as larvae under the ground ; some are found in 

 the earth collected in hollow, rotten stumps ; others (as Systenus) 

 in wood undergoing a process of dry decaying. 



After all that has been said above, the natural characters of the 

 Dolichopodidde may be put down as follows : Generally metallic 

 green, brisk and restless diptera of small or medium size, preda- 

 tory on other insects and living principally in damp situations ; 

 the male sex are principally distinguished from the females by 

 differences in the structure of the feet ; the larvae living under 

 ground or in decaying wood. Head hemispherical, eyes large, 

 usually not contiguous in both sexes, hairy, fenced in, along the 

 hind border with a row of bristles or hairs. Front, with bristles on 

 the vertex only, and with three ocelli. Antennae stretched out 

 straight, with a two-jointed arista. Face, without mystacine 

 bristles ; its inferior border not merging into the lateral border of 

 the mouth. Oral opening occupying the whole underside of the 

 head, and often also a considerable portion of its hind plane. 

 Proboscis short and stout, concealed above by the single-jointed, 

 usually scale-shaped palpi, with a wide opening which can be shut 

 by the protruding suctorial flaps. Labrum short and stout, with 

 coarse tooth-like excisions on the sides ; lingua much more slender 



