AMERICAN DIPTERA. 213 



cell narrowed, closed at the margin, or petiolate, the second 

 projecting into the first, the third much broader than long, 

 equaling in width the discal and the fourth posterior cells 

 together, the fourth at the very extremity very oblique, and 

 on the same line as the extremity of the discal cell, the latter 

 long and narrow, the anal cell closed at the margin. Face 

 broad, but slightly and evenly swollen, facial orbits parallel, 

 frontal orbits emarginate and beset with short forward directed 

 bristles. Mystax composed of fine hairs, strong bristles, or a 

 mixture of both; when of the first the fine hair extending 

 upward to the base of the antennas. Segments 1 and 2 of the 

 antennas subequal, cylindrical, segment 2 more slender and 

 slightly swollen distally; segment 3 attenuated at base, thence 

 fusiform, style very short, hardly perceptible. Occipital bris- 

 tles well developed. Thoracic dorsum with microscopic hair, 

 bristles only on the lateral margins above the base of the 

 wings, and on the posterior callosities; scutellum with two 

 bristles. Trichostical bristles present. Abdomen elongate, 

 slightly tapering, without bristles except on the lateral mar- 

 gins of the first segment, but with microscopic hair; hypo- 

 pygium small, ovipositor with a circlet of spines. Fore tibiae 

 without a terminal claw-like spur. 



Type. — Dasypogon venosus Wiedemann. 



Microstylum is represented in North America north of Mex- 

 ico by two species, galactodes and morosum, the latter being 

 our largest Asilid now known. As in both our species, the 

 mystax is confined to the oral margin and is composed chiefly 

 of stout bristles; they naturally fall under that division of 

 the genus which Loew, in his Dipterenfauna Sudafrika's char- 

 acterizes as " Knebelbart armharrig, mit ausserst dicken Borsten 

 durchmengt." 



SYNOPSIS OF SPECIES. 

 Wings more or less milky white; head, and thoracic dorsum evenly 



whitish pruinose galactodes. 



Wings blackish or yellowish-brown; bloom of thoracic dorsum 



prominent only on the lateral margins morosum. 



Microstylum galactodes. 



Microstylum galactodes Loew, Cent., VII, 44, I860. 

 cf 9- — Length 30-34 mm. — Dark reddish-brown species with thorax 

 whitish pruinose and wings more or less milky-white. 



TRANS. AM. ENT. SOC, XXXV. JUNE, 1909. 



