"Frons of male occupying a fourth part of the breadth of the head. Frontal stripe of female narrow in front, so broad behind that it entirely fills up the width of the frons. The dorsal region of the thorax dusty grey in color with four equally broad longitudinal stripes. Scutellum gray with black sides. The light regions of the abdomen yellowish, transparent, the darkest parts at least at the base of the ventral side yellow. The last segment and a dorsal line blackish brown. Seen from behind and against the light, the whole abdomen shimmering yellow, and only on each side of the dorsal line on each segment a dull transverse band. The lower part of the face silky yellow, shot with blackish brown. Median stripe velvety black. Antennæ brown. Palpi black. Legs blackish brown. Wings tinged with pale gray with yellowish base. The female has a broad velvety back, often reddishly shimmering frontal stripe, which is not broader at the anterior end than at the bases of the antennæ, but become so very much broader above that the light dustiness of the sides is entirely obliterated. The abdomen gradually becoming darker. The shimmering areas on the separate segments generally brownish. All the other parts are the same as in the male." The other species of flies found in houses in the Eastern United States which are frequently mistaken for the house or typhoid fly may readily be distinguished by the characters of the following key: _a._ Apical cell (R_5) of the wide wing open, i.e., the bounding veins parallel or divergent (fig. 100). Their larvæ are flattened, the intermediate body segments each fringed with fleshy, more or less spinose, processes. _Fannia_ b. Male with the sides of the second and third abdominal segments translucent yellowish. The larva with three pairs of nearly equal spiniferous appendages on each segment, arranged in a longitudinal series and in addition two pairs of series of smaller processes (fig. 100) _F. canicularis_ bb. Male with blackish abdomen, middle tibia with a tubercle beyond the middle. The larva with spiniferous appendages of which the dorsal and ventral series are short, the lateral series long and feathered (fig. 101) _F. scalaris_ aa. Apical cell (R) of the wing more or less narrowed in the margin; i. e., the bounding veins more or less converging (fig. 108). b. The mouth-parts produced and pointed, fitted for piercing. c. Palpi much shorter than the proboscis; a brownish gray fly, its thorax with three rather broad whitish stripes; on each border of the middle stripe and on the mesal borders of the lateral stripes is a blackish brown line. Abdomen yellowish brown; on the second, third and fourth segments are three brown spots which may be faint or even absent. The larvæ live in dung. The stable-fly (fig. 110) _Stomoxys calcitrans_