ii. Face linear; small basal cell of the wing absent. One species, _P. furcatum_, from California. _Parasimulium_ Malloch gg. Flies of a different structure. h. Antennæ composed of apparently two segments and a terminal arista formed of a number of closely united segments. Rare flies with aquatic larvæ. ORPHNEPHILIDÆ hh. Antennæ of six to fifteen segments, those of the male usually plumose; legs frequently slender and wings narrow CHIRONOMIDÆ i. Media forked (except in the European genus _Brachypogon_); thorax without longitudinal fissure and not produced over the head (except in four exotic genera); antennæ usually fourteen-jointed in both sexes; fore tibia with a simple comb of setulæ, hind tibia with two unequal combs, middle tibia without comb. CERATOPOGONINÆ j. Thorax produced cap-like over the head, wing narrow and very long. _Jenkinsia_, _Macroptilum_ and _Calyptopogon_, eastern hemisphere; _Paryphoconus_, Brazil. jj. Thorax not produced over the head. k. Eyes pubescent, empodium well developed, or if short then R_{2+3} distinct and crossvein-like or the branches of R coalescent; r-m crossvein present; fore femora not thickened; wing either with appressed hairs or with microscopic erect setulæ _Dasyhelea_ Kieff. kk. Eyes bare, or otherwise differing from the foregoing. l. Empodium well developed, nearly as long as the claws and with long hairs at the base; femora and fifth tarsal segments unarmed, i.e. without spines or stout setæ; fourth tarsal segment cylindrical. m. Wing with erect and microscopic setulæ. Widely distributed. (= Atrichopogon) _Ceratopogon_ Meig. mm. Wing with long and depressed hairs. Widely distributed. _Forcipomyia_ n. Hind metatarsus shorter or not longer than the following (i.e. the second tarsal) segment. Subgenus _Prohelea_ Kieff nn. Hind metatarsus longer than the following segment. Subgenus _Forcipomyia_ Meig.