(Figs. 9a–e)
[Key locator: Key to Group B species, couplet 17 (16)]
Heteragrion chrysops: Calvert 1901: 62–64 (misidentification; key to species, ♁ and ♀ in couplet 3; described morphological and coloration differences with H. tricellulare).
Heteragrion alienum: Williamson 1919: 13, 33–34 (key to species, ♁ in couplet d2, ♀ in couplet d2; description as a new species by coloration characters, based on material from Guatemala; comparison with H. albifrons and H. chrysops; figs. 5, 37, 38, 39, 57, 68, 88, 89, 105, 152, 153);— Paulson 1981: 303–304 (comparison of coloration patterns with other Heteragrion species);— Gonzalez-Soriano et al. 1982: 56 (record in Los Tuxtlas, Mexico);— Novelo-Gutiérrez 1987: 11–22 (description of F0 larvae);— Garrison et al. 2010: 88–89 (list of Heteragrion species; figs. 371, 376–378);— Rodríguez-Tapia et al. 2022: 274 (listed among species with an index of environmental vulnerability);— Carrillo-Muñoz & García-Miranda 2022: 196–203 (species list from Mexico).
Material examined. 2♁♁ MEXICO, Veracruz, “Los Tuxtlas”, Arroyo Tatocapán, 29.viii.1958, G.H. & A.F. Beatty leg., ABMM (two males in the same envelope).
Known distribution. Guatemala, Southern Honduras (Dennis Paulson pers. comm.) and Mexico.
Diagnosis and remarks. Regarding cercus morphology, H. alienum is close to H. chrysops, H. valgum, H. calendulum and H. eboratum, with which it shares the MP ridge bearing only small teeth and not partially covering ML. This species can be separated from these and other Group B species by the following character combination: BP the longest cercus portion in length (Figs. 9c–e); ridge above ML consisting of very small denticles, not partially covering ML (Fig. 9e); ML bearing no teeth or carina on its plate (Fig. 9e); AP longer than MP, bearing a longitudinal depression (Fig. 9c).