158 DIPTERA. 
1. Didyma mesta, sp.n., ¢ 2. 
Black, opaque ; thorax without stripes; abdomen greyish-pollinose, with discal and marginal macrochete. 
Length 5-5-6°5 millim. 
Front slightly prominent, in the male scarcely as broad as the eyes, in the female broader, in both sexes 
black with a silvery-white reflection, which, however, is not extended to the vertex; frontal band black, 
narrower than the lateral portions ; frontal bristles on each side in a curved row, descending as far as 
the end of the second antennal joint; the bristles on the vertex and two lateral ones (orbital bristles), 
which are directed forwards, more robust. Eyes densely clothed with yellowish pile. Face and cheeks 
blackish, with a white reflection ; the oral margin and the lower part of the cheeks (beneath the eyes) 
have a rufous reflection; bristles on the facial ridges mounting to half the face; vibrisse inserted 
near the oral margin. Antenne black, not fully reaching the vibrisse; third joint four times as long as 
the second, truncate at the end; arista thickened at the base. Proboscis black ; palpi cylindrical, black, 
the tip more or less rufous. Thorax black, opaque (seen from the front, the thoracic dorsum appears 
somewhat cinereous), without trace of stripes; scutellum black, with whitish-grey tomentum. Abdomen 
ovate, black; the second and following segments with whitish-grey tomentum, narrow white front 
margins, and not very long discal and marginal macrocheta. Legs black; front tibiee outwardly with a 
row of short bristles; middle tibia with some long bristles; hind tibie outwardly with many bristles 
and a longer one below the middle. Tegule whitish, brownish at the base. Wings nearly hyaline; 
small cross-vein a little before the middle of the discal cell; apical cross-vein straight ; posterior cross- 
vein curved. 
Hab. Mexico, Chilpancingo 4600 feet, Amula 6000 feet, Xucumanatlan 7000 feet, 
and Omilteme 8000 feet, all in Guerrero (H. H. Smith). 
Several males and one female. 
2. Didyma nigricolor, sp. n., ¢ 2. 
Shining black, pilose; abdomen with narrow whitish front borders to the segments, without discal macro- 
cheetee ; palpi black. 
Length 4—4°5 millim. 
Head black, the face with some grey reflections ; front narrower than the eyes; frontal bristles descending as 
far as the end of the second antennal joint; eyes densely pilose. Antenne black, shorter than the 
face; third joint four times as long as the second ; arista thickened not fully to half its length; palpi 
black, sometimes more or less rufous at the tip. Thorax and scutellum black, without grey tomentum 
or stripes. Abdomen conical (in the female a little broader), shining black, densely beset with black 
pile, with narrow whitish front borders to the second and following segments; macrochet short, less 
conspicnous among the hairs and only at the hind margins of the second and third segments. Legs 
black ; hind tibise outwardly with a row of bristles. Tegule and wings greyish-hyaline ; small cross-vein 
a little before the middle of the discal cell ; apical and posterior cross-veins nearly straight. 
Hab. Mexico, Atoyac in Vera Cruz, Teapa in Tabasco (H. H. Smith); Costa Rica, 
Volcan de Irazu 6000 to 7000 feet (Rogers). 
Two male and three female specimens. 
8. Didyma ambulatrix, sp. n., (2%). 
Blackish ; front and cheeks ochraceous ; thorax anteriorly greyish, with black stripes; abdominal segments 
with whitish front borders, and with long marginal and shorter discal macrochete. 
Length 5°5 millim. 
Front not prominent, ochraceous, as broad as the eyes, with parallel sides ; frontal band blackish, as broad as 
