jj. Squamæ well developed, usually large, the lower one frequently projecting from below the upper one; both posthumeral and intraalar macrochætæ present; thorax with a complete transverse suture; postalar callus present and separated by a distinct suture from the dorsum of the thorax; front of the female broad, of the male frequently narrow, the eyes then nearly or quite contiguous; the connectiva adjoining the ventral sclerites either visible or not; hypopleural macrochætæ present or absent; subcosta always distinct in its whole course, R_1 never short. CALYPTRATE MUSCOIDEA[J] k. Oral opening small, mouth parts usually much reduced or vestigial. This family is undoubtedly of polyphyletic origin but for convenience it is here considered as a single family. OESTRIDÆ. l. The costal vein ends at the tip of R_{4+5}, M_{1+2} straight, not reaching the wing margin, hence cell R_5 wide open (fig. 163j); squamæ small; arista bare; ovipositor of the female elongate. Larvæ in the alimentary canal of horses, etc. GASTROPHILUS m. Posterior crossvein (m-cu) wanting; wings smoky or with clouds. Europe. G. PECORUM mm. Posterior crossvein (m-cu) present, at least in part. n. Wing hyaline with smoky median cross band, and two or three spots; posterior trochanters with hook in the male and a prominence in the female. World wide distribution. G. EQUI. nn. Wings without spots. o. Posterior crossvein (m-cu) distad of the anterior crossvein (r-m); legs, particularly the femora, blackish brown. Europe and North America. G. HÆMORRHOIDALIS oo. Posterior crossvein opposite or proximad of the anterior crossvein. Europe and North America. G. NASALIS ll. The costal vein ends at the tip of M_{1+2}, M_{1+2} with a bend, the cell R_5 hence much narrowed in the margin, or closed.