Figs. 4 A–E
Macronema arcuatum Erichson 1848: 586 [type locality: by inference, “British-Guiana”; MCZ; ♂]. Flint 1974: 105, 106, Plate 1 [♂; distribution; wings]; Flint 1978: 388, 412, 416 [distribution; ♂; wings];
Pseudomacronema arcuatum (Erichson 1848); Ulmer 1907 a: 40, Plate 1 [wings; ♂]; Mosely 1931: 170 [distribution]; Fischer 1963: 163 [bibliography, distribution].
Macrostemum arcuatum (Erichson 1848); Flint 1996: 412 [distribution]; Flint et al. 1999: 68 [taxonomic notes; distribution]; Paprocki et al. 2004: 8 [distribution]; Nogueira & Cabette 2011: 349 [distribution].
Macrostemum arcuatum is unique and unmistakable among species of Macrostemum. The characters that differentiate this species from all others include one quadrate wart on the dorsal proximal region of abdominal segment X and a phallotremal sclerite bearing a pair of laminated dorsal processes. In addition, a distinctly hyaline N-shaped patch on the medial area of each forewing aids in its identification.
Synopsis. Adults pinned. Forewing mean length 9.9 mm (9.43–10.85 mm, n= 35). Head brown, with or without yellow spot behind eyes. Compound eyes brown. Scapes golden, with brown setae. Maxillary palps golden, with golden setae. Prothorax golden. Meso- and metathorax dark brown, with lateral light brown spots. Legs golden. Tibial spur formula 2,4, 4. Forewings dark, with hyaline marks, each bearing distinct hyaline N-shaped spot on medial area; discoidal cell absent; radial sector markedly expanded (Fig. 4 A).
Male genitalia. Abdominal segment IX, in lateral view, with anterior and posterior margins sinuous; posterior margins deeply notched above middle and with long setae bordering margin above and below notch on each side (Fig. 4 B); in dorsal view with posterior margin bearing medial truncate keel and long setae along right and left posterior margins (Fig. 4 E). Segment X, in dorsal view, bilobed, each lobe apically rounded and with subapical wart (Fig. 4 E); in lateral view, tapered to rounded apex with one quadrate subdorsal wart on each side near base (Fig. 4 B). Inferior appendages almost uniformly wide and covered uniformly by small setae; each with basal segment approximately two times length of apical segment, with longer setae at dorsal apex of basal segment, apical segment slightly upcurved and apically blunt (Fig. 4 B). Phallus arched near base; apex, in lateral view, truncate, with rectilinear posteroventral prominence (Fig. 4 C); phallotremal sclerite slender, bearing pair of laminated anterodorsal processes, with medial portion straight, transverse, and ends curved anterolateral (Fig. 4 D); phallotrema rounded, concave, on posterior apex of phallus (Fig. 4 D).
Material examined. BRAZIL: Amazonas: Barcelos, Serrinha, Rio Aracá, 0 0o 24 ’39,7’’N, 63 º 23 ’ 12 ’’W, 28.vii. 2009, luz do barco, A. Pes leg., 2 males (alcohol; INPA); Mato Grosso: Nova Olimpia, Fazenda Bandeirantes, Usinas Itamarati, Rio Bugres, 26.xii. 2002, luz, A. R. Calor & C. T. Salgado leg., 7 females (pinned; UFBA); Ribeirão Cascalheira, 1 º córrego (estrada Fazenda Manaus), 2.xii. 2006, luz, Calor & Silva leg., 1 male (pinned; UFBA); same data, 19 females (pinned; UFBA); same data except, 1.xii.2006, 6 females (pinned; UFBA); same data except Córrego Represa, 27.xi. 2006, luz, Calor, Silva, Mateus leg., 1 female (pinned; UFBA); Tangará da Serra, Fazenda Calcário Tangará, Grupo Itamarati, Rio Sepotuba, 3.i. 2003, puçá, A. R. Calor leg., 1 female (pinned; UFBA); Pará: Rio Xingu, Camp (3 º 39 ’S, 52 º 22 ’W), ca 60 km S. Altamira, x. 1986, P. Spangler & O. Flint leg., 2 males, 13 females (pinned; MZSP); (?) State [Mato Grosso State]: estrada da colônia, Aripuanã, Y. T., 22.i. 1975, L. P Albuq. & E. L. Antony leg., 1 male (pinned; INPA); SURINAM: Marowijne: Benzdorp, Rio Lawa, xi. 1963, B. Malkin leg., 2 males (alcohol; MZSP).
Distribution. Brazil (AM, MT, PA), Guyana, Peru and Surinam.