f. a.n.a.l cell closed at apical margin by the a.n.a.l crossvein.
g. Ocelli absent. _Stilbometopa_ Coq.
gg. Ocelli present.
h. R_{4+5} does not form an angle at the crossvein. On birds. There is a record of one species of this genus attacking man. ORNITHOMYIA Latr.
hh. R_{4+5} makes an angle at the crossvein. _O.
confluens_. _Ornithoica_ Rdi.
ff. a.n.a.l cell not closed by an a.n.a.l crossvein. _Lynchia_, _Pseudolfersia_, and _Olfersia_ are chiefly bird parasites. The first mentioned genus is said to be the intermediate host of _Haemoproteus columbae_.
aa. Abdominal segments chitinous; not parasitic in the adult stage.
b. Antennae with six or more segments and empodium not developed pulvilliform; palpi often with four segments.
c. Ocelli present. BLEPHAROCERIDae, RHYPHIDae, BIBIONIDae, MYCETOPHILIDae, besides some isolated genera of other families.
cc. Ocelli absent.
d. Dorsum of the thorax with a V-shaped suture; wings usually with numerous veins; legs often very long and slender. Crane flies.
TIPULIDae
dd. Dorsum of the thorax without a V-shaped suture.
e. Not more than four longitudinal veins ending in the wing margin; wing usually hairy: antennae slender; c.o.xae not long; tibiae: without spurs, legs long and slender. Small, delicate flies often called Gall gnats. CECIDOMYIIDae.
ee. More than four longitudinal veins ending in the wing margin.
f. The costal vein is not produced beyond the tip of the wing; radius with not more than three branches.
g. Antennae short, composed of ten or eleven closely united segments; legs stout; body stout; abdomen oval; anterior veins stout, posterior ones weak (fig. 163 b); eyes of the male contiguous over the antennae. Black flies, buffalo flies, turkey gnats. Many North American species, several of them notorious for their blood sucking propensities. SIMULIIDae
h. Second joint of the hind tarsus with basal scale-like process and dorsal excision (fig. 161 h); radial sector not forked; no small cell at the base of the wing. _S. forbesi_, _jenningsi_, _johannseni_, _meridionale_, _piscicidium_, VENUSTUM, VITTATUM, etc.
Widely distributed species (= EUSIMULIUM) SIMULIUM Latr.
hh. No basal scale-like process on the second joint of the hind tarsus; radial sector usually forked (fig. 163 b).
i. Face broad, small basal cell of the wing present. _P.
fulvum_, HIRTIPES, _mutatum_, PECUARUM, _pleurale_.
PROSIMULIUM Roub.
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. Antennae composed of apparently two segments and a terminal arista formed of a number of closely united segments. Rare flies with aquatic larvae.
ORPHNEPHILIDae
hh. Antennae of six to fifteen segments, those of the male usually plumose; legs frequently slender and wings narrow CHIRONOMIDae
i. Media forked (except in the European genus _Brachypogon_); thorax without longitudinal fissure and not produced over the head (except in four exotic genera); antennae usually fourteen-jointed in both s.e.xes; fore tibia with a simple comb of setulae, hind tibia with two unequal combs, middle tibia without comb. CERATOPOGONINae
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 p.u.b.escent, 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 setulae _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 setae; fourth tarsal segment cylindrical.
m. Wing with erect and microscopic setulae.
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.
ll. Empodium short, scarcely reaching the middle of the claws, or vestigial.
m. R-m crossvein wanting.
n. Palpi four segmented; inferior fork of the media obliterated at the base. Australia.
_Leptoconops_ Skuse
nn. Palpi three-segmented.
o. Legs spinulose, tarsal claws of the female with a basal tooth or strong bristle, those of the male unequal, the anterior with a long sinuous tooth, the posterior with a short arcuate tooth.
Italy. MYCTEROTYPUS Noe
oo. Legs unarmed; no crossvein between the branches of the radius (fig. 163e). New Mexico. TERSESTHES Townsend
mm. R-m crossvein present.
n. Fore femora very much swollen, armed with spines below, fore tibia arcuate and applied closely to the inferior margin of the femur.
o. R_{2+3} present, therefore cell R_1 and R_2 both present; wing usually fasciate.
United States _Heteromyia_ Say.
oo. R_{2+3} not distinct from R_{4+5}, hence cell R_3 obliterated. South America _Pachyleptus_ Arrib. (Walker)
nn. Fore femur not distinctly swollen.