130 DIPTERA OF NORTH AMERICA. 



usual. The hypopygiura of the male, which attains a considerable 

 size in some species only, is turned down, and generally, together 

 with the small sixth segment, encompassed by the lateral border of 

 the fifth abdominal segment bending down over it. The anal ex- 

 tremity of the female, except in a few species, is entirely retracted ; 

 for this reason, the sexual difference of many species is somewhat 

 difficult to ascertain on examining single dry specimens. Wings 

 on their whole surface covered with microscopical hair ; the costal 

 vein consists of three parts, the first of which reaches from the base 

 to a little beyond the transverse humeral vein, which, quite in its 

 neighborhood, runs over to the costa; the second from thence to 

 the tip of the first longitudinal vein, where the third begins. 

 These three parts of the costal vein are not to be confounded with 

 the three segments of the costal vein so frequently used in charac- 

 terizing the species; the latter are reckoned from the base of the 

 wing to the tip of the first longitudinal vein, from thence to the 

 tip of the second longitudinal vein, and from this to the tip of the 

 third longitudinal vein. The auxiliary vein is distinct only at its 

 very base and then coalesces with the first longitudinal vein ; the 

 second basal cell, i. e. the anterior of the two small basal cells, unites 

 with the discoidal cell, the ordinary separating vein disappearing, 

 so that the discoidal cell apparently reaches very far towards the 

 base of the wings; it is not at all unusual, that on a closer examina- 

 tion a rudiment of the obliterated transverse vein may be seen ; 

 the posterior of the two small basal cells or anal cell is generally 

 imperfect and very small. Alula; small. Legs slightly bristled ; 

 in some genera the species have some longer bristles on the upper 

 side of the intermediate tibia?, which in all genera are provided 

 with spurs. 



Most of the species, if not all, live in the neighborhood of water 

 or in moist places. I have observed many years ago, that the 

 food of several species chiefly consists of Infusoria. The larva' of 

 those European species, the metamorphosis of which is known, 

 live, at least by far most of them, in water, some exclusively in 

 water which is very decidedly salt; two of them are leaf-miners. 



General division of the UpJ/ydrinfdae. 



In order to facilitate the determination of the already numerous 

 genera of Ephydrinida it will be useful to subdivide this family in 

 Several sections, which may be done as follows: — 



