Diptera. 67 



present; front of male narrow or the eyes meeting; auxiliary vein always 



distinct, first vein never short. (SCHIZOMETOPA, CALYPTERATJE.) 41 



Lower calypter vestigial or wanting; posthumeral bristle present only in some 

 Scatophagidae; thorax without a complete transverse suture, posterior 

 callosity usually absent; a visible membrane connecting the dorsal and 

 ventral segments; front of both sexes of equal width, or if wider in the female, 

 the greater width is due to a widening of the middle strip; fourth vein nearly 

 straight, if curved never with an appendage; often very small species. 

 (HOLOMETOPA, ACALYPTERAT^E; BORBOROIDEA.) 51 



41. Mouth opening small, the mouth-parts wanting or vestigial, not functional; 



vibrissse and bristles absent, no sternopleural bristles; ventral membrane 



evident, at least at the base of the abdomen. Bot-flies 42 



Mouth opening normal, the mouth-parts functional; usually with sternopleural 

 bristles at least 43 



42. No hypopleural bristles or hairs; costa extending to the third vein; first posterior 



cell very widely open; calypteres rather small. (Gastrophilus [G. equi, 



Horse Bot-fly].) GASTROPHILIIXE 



Hypopleurse bearing hairs or bristles; costa extending to the fourth vein; first 

 posterior cell closed or narrowed; calypteres large. (CEstrus [CE. ovis* 

 Sheep Bot-fly], Hypoderma [H. lineata, Ox warble], Cuterebra) (including 

 HYPODERMATlDjE, CUTEREBRID&) (ESTRID^E 



43. Both hypopleural and pteropleural bristles or hairs present in a more or less 



vertical row; fourth vein bending or curving forward; when three sterno- 

 pleural bristles usually but one behind. (TACHINOIDEA.) 44 



Either the hypopleural or pteropleural hairs or bristles or both absent; ventral 

 membrane usually distinct; when three sternopleural bristles present usually 

 two behind 50 



44. Facial plate more or less convexly produced nose-like below the vibrissal angles 



and fused with the lowest part (epistome); ventral membrane present; 

 abdomen destitute of stout bristles. (A16phora, Phorantha, Cistogaster, 

 Trich6poda) (including GYMNOSOMATID.E with four, not five abdominal 



segments) PHASinXE 



Facial plate flattened, at most slightly produced; ventral membrane not visible; 

 abdomen bearing some stout bristles 45 



45. Facial plate receding and short, the cheeks very broad, vibrissse located near 



the middle of the face; antennae short. (Microphthalma.) 



MEGAPROSOPHXE 



Facial plate long and never conspicuously receding, the oral margin more or 

 less prominent, vibrissal angles near the oral margin; antennas usually long, 46 



46. Second ventral segment of the abdomen more or less overlapping the edges of 



the dorsal segment 47 



Edges of the dorsal segments overlapping all the ventral ones 49 



47. Hindermost posthumeral bristle located lateral to the presutural bristle; fifth 



ventral segment of the male with a split hind margin, sometimes strongly 

 developed; usually metallic and with plumose arista. (Callfphora [Blow- 



