ii. Eyes bare; fronto-orbital macrochaetae in a double row, antennae contiguous at the base.
j. One or more pairs of well developed anterior inner dorsocentral (acrostichal) macrochaetae; seta on extensor surface of hind tibia. M. a.s.sIMILIS, STABULANS, etc. Europe and America. MUSCINA R. D.
jj. Anterior inner dorsocentrals and the setae; on the extensor surface of the hind tibia wanting. _M.
micans_, etc. Europe and North America. _Morellia_ R. D.
ff. Squamula thoracalis not broadened mesad and caudad, not reaching the margin of the scutellum; macrochaetae on extensor surface of the hind tibia wanting.
g. Eyes p.u.b.escent. _M. meditabunda._ Europe and America.
_Myiospila_ Rdi.
gg. Eyes bare; R_1 ends before the middle of the wing. A number of species from the tropics of both hemispheres.
_Clinopera_ V. d. W.
bb. Hypopleurae with a vertical row of macrochaetae.
c. Eyes p.u.b.escent.
d. R_1 ends about opposite the r-m crossvein; basal section of R_{4+5} bristly nearly to the crossvein; _S. enigmatica_.
Africa. _Somalia_ Hough
dd. R_1 ends distad of the r-m crossvein.
e. Eastern hemisphere. Australasia. _N. ochracea_, _dasypthalma_.
_Neocalliphora_ Br.
ee. Western Hemisphere. _T. muscinum._ Mexico. _Tyreomma_ V. d.
W.
cc. Eyes bare.
d. The vibrissal angle situated at a noticeable distance above the level of the margin of the mouth.
e. Sternopleural macrochaetae arranged in the order 1:1.
f. Genae with microchaetae.
g. Body grayish, with depressed yellow woolly hair among the macrochaetae; wings folded longitudinally over the body when at rest. Cl.u.s.ter flies. _P. rudis_ and related species, widely distributed. _Pollenia_ R. D.[N]
gg. Body metallic blue or green. Eastern Hemisphere.
h. Vibrissal angle placed very high above the oral margin; a carina between the antennae; outer posthumeral wanting; anterior intraalar present. _T. viridaurea_.
Java. _Thelychaeta_ Br.
[Ill.u.s.tration: 167. Horn fly. (_a_) egg; (_b_) larva; (_c_) puparium; (_d_) adult. (4). Bureau of Entomology]
hh. Vibrissal angle moderately high above the oral margin; carina small or wanting; no post humeral macrochaeta; lower squamae hairy above. (= _Paracompsomyia_ Hough) (fig. 166). _Pycnosoma_ Br.
ff. Genae bare. _S. terminata_. Eastern Hemisphere _Strongyloneura_ Bigot
ee. Sternopleurals arranged 2:1.
f. Body metallic green or blue, with gray stripes; genae hairy to the lower margin; post humerals often wanting; lower squamae bare above. (= _Compsomyia_ Rdi.). CHRYSOMYIA R. D.
g. With one or two orbitals; height of bucca less than half the height of the eye. South and east U. S. (fig. 107).
C. MARCELLARIA
gg. No orbitals; height of bucca about a third less than height of eye. West U. S. _C. wheeleri_ Hough
ff. Body black or sordidly metallic greenish gray, usually yellow pollinose or variegate; genae at most hairy above.
_N. stygia_. Eastern Hemisphere. _Neopollenia_ Br.
dd. Vibrissal angle situated nearly on a level of the oral margin.
e. Species wholly blackish, bluish, or greenish metallic in color.
f. First section of R_{4+5} with at most three or four small bristles at the immediate base.
g. The bend of M_{1+2} a gentle curve; costal spine present; cell R_5 closed, ending before the apex of the wing. _S.
cuprina._ Java. _Synamphoneura_ Bigot
gg. Bend of M_{1+2} angular; or the insect differs in other characters; dorsal surface of the squamula thoracalis hairy (except in _Melinda_); arista plumose only on the basal two-thirds (except usually in _Calliphora_ and _Eucalliphora_).
[Ill.u.s.tration: 168. Head of horn-fly (Lyperosia irritans); (_a_) female; (_b_) male; (_c_) lateral aspect of female. Bureau of Entomology.]
h. Arista plumose only on the basal two-thirds.
i. Base of the antennae ventrad of the middle of the eye; eyes of the male nearly contiguous; genae hairy; second abdominal segment with median marginal macrochaetae; two, rarely three, postsutural intraalar macrochaetae.
j. Squamula thoracalis dorsally with long black hairs; male hypopygium two-segmented, large, projecting; claws and pulvilli of the male elongate; three strong sternopleural macrochaetae; genae at least half the width of the eye; buccae (cheeks) half the height of the eyes; oviviparous. _O. sepulcralis._ Europe. _Onesia_ R. D.
jj. Dorsal surface of the squamula thoracalis bare; male hypopygium small, scarcely projecting below; claws and pulvilli not elongate; two stout sternopleural macrochaetae, sometimes with a delicate one below the anterior; genae nearly linear in the male; buccae about a third of the eye height; oviparous. _M. caerulea_. Europe.
_Melinda_. R. D.
[Ill.u.s.tration: 169. Lateral and dorsal aspects of the thorax, and frontal aspect of the head of a muscoidean fly, with designations of the parts commonly used in taxonomic work.]
ii. Base of the antennae dorsad of the middle of the eye; eyes of both s.e.xes distinctly separated; dorsal surface of the squamula thoracalis with black hairs; two postsutural intraalar macrochaetae.
j. Hypopygium of the male large, with a pair of slightly curved forceps whose ends are concealed in a longitudinal slit in the fifth ventral sclerite; third posterior inner dorso-central (acrostichal) macrochaetae absent; anterior intraalar rarely present; abdomen usually not pollinose; the second segment without median marginal macrochaetae; face yellow. _C. mortuorum_, _cadaverina_, and related species. Both hemispheres. _Cynomyia_ R. D.[O]
[Ill.u.s.tration: 170. Sepsis violacea; puparium and adult. (See page 297.) After Howard.]
jj. Three pairs of posterior inner dorsocentrals (acrostichals) present; second abdominal segment with a row of marginal macrochaetae; genae hairy, at least above.
k. Hypopygium of the male with a projecting style.
_S. stylifera_. Europe. _Steringomyia_ Pok.