(Figs. 60a–g)

[Key locator: Key to Group A species, couplet 8 (7)] Heteragrion silvarum:Sjöstedt1918:4–6 (description of♁ and ♀;comparison with H.aurantiacum, H.cinnamomeum and “ H. malicentum ” [misspelled]; plate 1, fig. 10);— Williamson 1919: 63–64 (discussion and comparison with other species);— De Marmels 1987: 229–231 (redescription of holotype and ♀ paratype, differences from H. ictericum, illustration of ♁ and ♀ head and prothorax, ♁ thorax, ♀ S 8–10 in lateral view, ♀ S 9–10 in ventral view; figs. 13–19, 47–48);— Lencioni 2005: 141 (data on description and distribution, illustration from Sĵstedt 1918 and De Marmels 1987; figs. 88a–j);— Garrison et al. 2010: 88 (list of Heteragrion species);— von Ellenrieder 2012: 59, 62, 73 (list of species from Suriname; mentions synonymy with H. melanurum);— Lencioni 2013: 13 (synonymic list, types, distribution, diagnosis, remarks; figs. 23, 33d–f, 54c, 72);— von Ellenrieder et al. 2017: 3 (list of species from Guyana);— Rochas et al. 2022: 200 (species recorded from French Guiana).

Heteragrion melanurum: Williamson 1919: 20–22 (key to species, ♁ in couplet c2; description of ♁; comparison with H. ictericum; figs. 9, 16, 76–77, 136);— Paulson 1981: 303 (comparison of coloration patterns with other Heteragrion species);— De Marmels 1987: 229–231 (proposed synonymy with H. silvarum).

Material examined. 1♁ BRAZIL, Pará state, Flona de Carajás, Igarapé Afluente do Rio Águas Claras, 22.viii.2022, (-5.9881, -50.4984, 240m asl), G. Desidério leg., INPA; 1♁ Tailândia, Agropalma, 7.iv.2012, J.M. B. Oliveira-Jr. leg., LABECO; 5♁♁ Tailândia, Agropalma (H48H50), 25.x.2016, (-2.6183, -48.8301), Vilela, Cordero-Rivera, Amorim & Rivas-Torres leg., LESTES; 4♁♁ same data, but (P1F1), 27.x.2016, (-2.6191, -48.7811); 3♁♁ same data, but (P10P2), 3.xi.2016, (-2.3116, -48.6692); 1♁ same data, but (P21P13 Novo), 4.xi.2016, (-2.2663, -48.6268); 1♁ same data, but (P24P14), 23.x.2016; (-2.5737, -48.8174); 1♁ Rondônia state, Porto Velho, 3.v.1922, (-8.7500, -63.9000, 100m asl), J.H. Williamson & J.W. Strohm leg., ABMM; 1♁ same data, but FAAL.

Synonyms. Heteragrion melanurum Williamson, 1919 (De Marmels 1987)

Known distribution. Brazil (states of Amazonas, Pará and Rondônia).

Diagnosis and remarks. This species shares with H. cooki and H. cinnamomeum the cercus with a long BP, ending in subequal MP and AP, with a developed ML. The following character combination distinguishes this species from the remainder of Group A species: straight BP margin (Fig. 60d); ML broad, roughly squared (Figs. 60d–g); ML ridge short, nearly straight, reaching or not ML apex (Fig. 60f); ML apex blunt, not bilobate; MP–AP junction rounded or angled (Figs. 60d–g).