32 MISC. PUBLICATION 6 31, U. S. DEPT. OF AGRICULTURE 



Antenna shorter than the thorax, with not more than 10 segments, those 

 beyond the second fused to form an apparently annulated third seg- 

 ment or a third segment with an apical style 5 



5. Body without distinct bristles or bristly hairs; wing veins tending to 



crowd toward the costal margin with the result that the discal cell 

 is usually small and located on the anterior half of the wing (fig. 



88 ) STRATIOMYIDAE 



Body with bristles, at least on the legs ; wing venation normal, the discal 

 cell relatively large and located on the posterior half of the wing 

 (fig. 3); vertex, from anterior view, not concave; 5 posterior 



Cells THEEEVIDAE 



6. Wing with a spurious vein, that is, a veinlike fold in the membrane be- 



tween the radius and media and transversing cross vein r-m (fig. 



91) SYRPHIDAE 



Wing without such a spurious vein 7 



7. Mouth parts vestigial (cf. fig. 61) 8 



Mouth parts well developed 11 



8. Postscutellum distinctly formed ; squamae large ; apical cell greatly nar- 



rowed or closed at its apex — 9 



Postscutellum undeveloped 10 



9. Apical cell closed and petiolate (fig. 62) oestbidae 



Apical cell open ^ hypodeematidae 



10. Squamae large; apical cell greatly narrowed at its apex (fig. 



47) cuteeebeidae 



Squamae small ; apical cell gradually broadening to the wing margin 

 (fig. 45) - gasterophilidae 



11. Wing with the anterior veins strong and the others oblique and weak 



(fig. 97) phoeidae 



Wing of the normal muscoid type, without unusual venation (cf. figs. 

 4 and 71) 12 



12. Second antennal segment with a longitudinal suture extending along its 



upper outer edge (cf. fig. 1) ; squamae usually large; postalar callus 



distinct 13 



Second antennal segment without a longitudinal suture ; squamae usually 

 small ; postalar callus not differentiated 16 



13. Postscutellum well developed laevaevobidae 



Postscutellum undeveloped 14 



14. Hypopleural bristles present; apical cell greatly narrowed toward its 



apex (fig. 4) 15 



Hypopleural bristles absent ; apical cell sometimes greatly narrowed to- 

 ward its apex (fig. 82) but often broadly open (figs. 71 and 78)__ mtjscidae 



15. Two notopleural bristles present ; body, in myiasis-producing species, 



either largely metallic blue, purple, or green, or largely tes- 

 taceous calliphoeidae 



Three or more notopleural bristles present ; body in myiasis-producing 

 species grayish, with either pollinose spots or a tesselated pattern on 

 the abdomen : saecophagidae 



16. Subcosta distinctly differentiated from vein r x and ending independently 



in the costa (fig. 96) 17 



Subcosta absent or only partly developed, not reaching the costa 19 



17. Metathoracic spiracle with 1 to several hairs, visible only under high 



magnification, on its border ; palpi vestigial sepsidae 



Metathoracic spiracle with only ordinary soft pubescence; palpi well 

 developed . 18 



18. Vibrissae present ; legs short piophilidae 



Vibrissae absent ; legs long and stiltlike tylidae 



19. Arista plumose (in species considered here) ; vibrissae present ; oral open- 



ing of moderate size. Small yellowish flies with a prominent facial 



carina and with black abdominal markings dbosophilidae 



Arista bare (in species considered here) ; vibrissae absent, but the face 

 may be bristly ; oral opening unusually large and gaping ephydeidae 



MATURE LARVAE 



1. Head distinct and sclerotized dorsally, though sometimes retractile into 

 the prothorax ; antennae distinctly developed and situated on a sclero- 

 tized plate ; no free cephalopharyngeal skeleton ; mandibles broad 2 



