(Figs. 10a–g)

[Key locator: Key to Group B species, couplet 29’]

Heteragrion angustipenne: Selys 1886: 64–65 (description of ♁ and brief description of ♀, from “ Équateur ”, comparison with other species, states that the male resembles H. aequatoriale and the female that of H. aequatoriale and H. icterops);— Calvert 1909: 108 (examination of ♁ specimen from Peru, comparison with original description; figs. 42–43);—Sĵstedt 1918: 8 (comparison with H. speciosum);— Williamson 1919: 36 (key to species, ♁ in couplet g3; states that the last segments of male holotype were lost; points out inconsistencies with Selys description of the ♀; figs; 29, 109, 110, 158);— Kimmins 1970: 196 (assigns a lectotype, states that the last segments were glued back, poss. by McLachlan);— Paulson 1981: 303–304 (comparison of coloration patterns with other Heteragrion species);— Garrison et al. 2010: 88, 91 (list of Heteragrion species; figs. 385–386);— Vilela et al. 2019a: 188, 192 (comparison with ♀ of H. icterops and H. bariai; key to ♀, couplet 1);— Stand-Pérez et al. 2019: 92–96 (key to species, ♁ in couplet 5’, ♀ in couplet 4; reports first record for Colombia; full description of ♀, variation among examined specimens; comparison with H. peregrinum; figs. 4c–d, 7d–f, 12d–f, 16f, j, 17).

Material examined. 1♁ BRAZIL, Rondônia state, Porto Velho, Caicala, 16.i.2014, A.L. Andrade & G. Nicácio leg., LABECO. 13♁♁ COLOMBIA, Putumayo Department, Mocoa Municipality, Quebrada Sangoyaco, (650m asl), L. Pérez, J, Montes & J. Villamil leg., UARC; 3♁♁ Vereda Los Sauces (600m asl), Pérez & J. Montes leg., UARC; 2♁♁ Serranía de los Churumbelos National Park, 26.i.2013, (1000m asl), UARC; 1♁ Putumayo Department, Orito Municipality, near Nuevo Mundo, (0.6725, -77.0798, 950m asl), M. Vigano leg., CEUA; 1♁ road to Nuevo Mundo island, 20.i.2017, (0.6613, -77.0767, 890m asl), M. Vigano, A. Corso, & O. Janni leg., CEUA.

Known distribution. Brazil (Amazonas and Rondônia states), Colombia (eastern Andean foothills), Ecuador, and Peru.

Diagnosis and remarks. As already highlighted by Selys (1886), Williamson (1919), and Stand-Pérez et al. (2019), Heteragrion angustipenne is very similar in morphology to H. aequatoriale, with which it shares the cleft on the ridge-ML junction and the ridge bearing two rows of strong teeth (Figs. 7f–h; Fig. 10f–h). Apart from these similarities, H. angustipenne can be separated from the remainder of Group B species by the following character combination: BP only slightly convex (Figs. 10d–g); ridge above ML nearly straight, long, with an additional row of teeth below the main ridge, partially covering ML in dorsal and dorsolateral views (Figs. 10d–g); ML with acute apex (Figs. 10d–g); MP–AP junction with a marked cleft (Fig. 10g).