Macrostomus arcucinctus (Bezzi, 1909)

(Figs 1 A–D)

Rhamphomyia arcucincta Bezzi, 1909: 331 (syntypes). Melander, 1928: 186; Collin, 1933: 211 (cit).

Macrostomus arcucinctus: Smith, 1961: 53; 1967: 29 (cat.); Rafael & Cumming, 2004: 446.

Diagnosis. Females of this species are distinguished by the thorax and abdomen subshiny dark brown to black with blue reflections; mesonotum densely gray pruinose. Legs mainly yellow to dark yellow. Mid femur with small posteroventral pennate setae on distal half. Apex of the wing infuscate; anal lobe narrow. Halter white. Abdomen shiny brown to black.

Redescription. Lectotype female. Body length from original description: “ 3.2 mm; wing length 3.0 mm”. Head narrowly dichoptic. Inferior facets slightly larger than superior ones. Frons shiny black. One pair of proclinate ocellar setae. Face gray pruinose, slightly narrower than frons. Postcranium narrow, gray pruinose, with blue reflection in certain light. Inner vertical seta stouter than outer vertical seta, latter subequal in length to uniseriate postocular row of setae; remaining occipital setae slightly shorter than postoculars and restricted to dorsal half. Antenna dark brown, gold pruinose, short pubescent. Proboscis yellow, as long as head height. Thorax subshiny dark brown to black with blue reflection, mesonotum densely gray pruinose, less pruinose medially on scutum. Thoracic chaetotaxy: 4 antepronotals weak; 1 postpronotal stout, 2–3 weak; 4 dorsocentrals; 1 presutural supra-alar; 0 postsutural supra-alar; 1 postalar; 2 small proepisternals; 3 notopleural, anterior seta weaker; 2 pairs of scutellars (broken); 8 laterotergitals. Legs yellow to dark yellow except distal tarsomeres darker. Legs longer setae: mid tibia with 1 dorsal at middle slightly stouter and 1 anteroventral, 1 posteroventral somewhat inconspicuous distally. Mid femur with posteroventral pennate setae on distal half, thinner than in other species with this kind of setae (originally described as “non pennatis”). Hind legs lost. Wings lost, described as: “ alis brevibus hyalinis, macula stigmatica at area apicali fuscis, angulo axillari valde aperto, cellula discoidali magna nervos duos primos praeter basin decolores emittente ” [wing hyaline slightly brown infuscated on pterostigma and apex of veins R 2+3 and R 4+5; anal lobe narrow, distinct, with axillary angle obtuse; veins M 1 and M 2 evanescent]. Halter white. Abdomen shiny brown to black, somewhat blue depending on angle of light incidence, with small setae. Sternites concolorous with tergites. Tergite 8 (Figs 1 A–B) subrectangular in dorsal view, with shallow basal and deeper distal sinus, basally with narrow sclerotized sub-basal band. Sternite 8 (Figs 1A, C) longer than respective tergite, higher at basal half in lateral view, slightly more sclerotized medially, with apex somewhat acute. Tergite 9+10, sternite 10 and cerci lost. Genital fork (Fig. 1D) short, Y-shaped. Genital chamber membranous.

Male. Unknown.

Geographical records. Bolivia (La Paz).

Type material examined. LECTOTYPE ♀ (here designated): “ BOLIVIA [La Paz], Mapiri, Sarampioni, 31.iii. 1903, 700 m. ” (SMTD).

Lectotype condition. Wings and hind legs lost. Abdomen in microvial with glycerin.

Remarks. The single remaining syntype specimen in the SMTD collection is designated lectotype accordingly to fix and stabilize the current concept of the name.