10 PROCEEDINGS OF THE NATIONAL MUSEUM. vou CO, 



except the base and lower corner which is yellow. Arista longer than 

 the face, black, thickened at base only, lamellae black, elliptical, with 

 a white elliptical spot on upper edge at the base. Thorax and scutel- 

 lum dark green bronze with a dark brown dust. Abdomen a lighter, 

 brassy green, coated with a golden brown dust. Hypopygium large, 

 pedicel whittish pruinose on upper side with a greenish reflection in 

 certain lights and slightly corrugated, shiny reddish-black below, 

 second joint from the side, triangular with whitish pruinosity and 

 long black hairs, last joint very large, heavily pruinose, basally with a 

 lavender tint, otherwise pale green with two smoother black dots in 

 the center, lower portion on the sides shiny reddish-black, lamellae 

 broad, pale yellow with long black hairs. Legs all yellow except 

 extreme tips of middle and hind tibiae and all tarsi, blackish. Front 

 femora with long, straight black hairs on lower side. Wings slender, 

 faintly tinged with brown ; tegulae pale yellow with long black cilia ; 

 halteres pale yellow. 



Female. — Very similar except the general color is slightly darker. 

 Face is more silvery, antennae shorter, third joint all black except a 

 very small area at lower corner, arista normal, not quite as long as 

 the face and brown in color, darker at the base. Orbital cilia whit- 

 ish close to the oral margin. Legs more reddish, apical two-thirds 

 of front tibiae blackish ; front coxae and a large spot on under side 

 of front femora, at the base, silvery gray. Infuscation on the tibiae 

 extends more on apical half, but is much darker on apical fourth. 



Length, 6 mm. 



Type locality. — St. Anthony, Idaho. Dr. J. M. Aldrich, collector. 



Described from three males and one female. Two males and the 

 female from St. Anthony, Idaho, July 16, 1900, and a male from 

 Soda Spring, Idaho, June, 1900, J. M. Aldrich, collector. 



Type., male. — Allotype^ female, and two paratypes. Cat. No. 24132, 

 U.S.N.M. 



Closely allied to T. auratus Aldrich, but easily separated by the 

 straight hairs on the front femora, the size of the antennae, the 

 small lamella of the arista and the hypopygium has two small dark 

 spots. This species is also larger in size than auratus. 



8. TACHYTRECHUS TENUISSTA, new spscies. 



Fig. 10. 



Male. — Face just above the middle about one-third to one-half the 

 width of the lower part and heavily coated with a golden brown 

 dust; front deep green, not very shiny, ocellar triangle black, ocelli 

 pale yellow. Orbital cilia and mouth parts black. Antennae en- 

 tirely yellow; first joint about twice the 'length of two and three 

 together; this joint has a thumblike projection on the inside near 

 the apex; second joint rudimentary; third joint quite short and 



