Key to adult males of the genus Cyrnellus 1. Subapicomesal spine I of each inferior appendage directed obliquely apicad with respect to longitudinal axis of inferior appendage (Fig. 6B)......................................................................................... 2 - Subapicomesal spine I directed perpendicularly to longitudinal axis of each inferior appendage (Fig. 3F)............... 4 2(1). Posterior margins of sternite IX convex and sinuous with slight undulations; subapicomesal spine I closer to apex of each inferior appendage and digitate (Figs 6A–6D, as).................................................... C. misionensis - Posterior margins of sternite IX irregular with some excisions and protuberances (Fig. 5A); subapicomesal spine I of each inferior appendage in mesal or subapical position (Fig. 5B, as)................................................. 3 3(2). Subapicomesal spine I of each inferior appendage mesally inserted, long and digitate (Figs 4E–4H).............. C. rianus - Subapicomesal spine I, subapically inserted, short and triangular (Figs 5A–5D)................................ C. risi 4(1). Subapicomesal spine of each inferior appendage triangular, acute (Figs 3F, 3I–3K)................................. 5 - Subapicomesal spine rounded or mammiform (Figs 2F, 6F), or with two subapicomesal points (Figs 1B, 2B, 5F, 7B)...... 9 5(4). Subapicomesal spine of each inferior appendage arising far from apex (Figs 3E–3K)...................... C. fraternus - Subapicomesal spine arising close to apex (Figs 1G, 3B, 4B)................................................... 6 6(5). Triangular subapicomesal spine of each inferior appendage flat (Figs 1F–1I)............................ C. boliviensis - Triangular subapicomesal spine circular in cross-section (Figs 3B, 4B).......................................... 7 7(6). Subapicomesal spine of each inferior appendage with wide base, forming equilateral triangle (Figs 3A–3D)... C. marginalis - Subapicomesal spine with narrow base, forming isosceles triangle (Fig. 4B)....................................... 8 8(7). Subapicomesal spine of each inferior appendage conspicuously subapical, inner lobe triangular (Figs 4A–4D).... C. minimus - Subapicomesal spine very near apex, inner lobe round (Chamorro-Lacayo 2003, fig. 2B)................ C. zapateriensis 9(4). Subapicomesal spine II of each inferior appendage absent, single subapicomesal spine with wide, globular base (Figs 2F, 6F).................................................................................................. 10 - Subapicomesal spines I & II present (Figs 1B, 2B, 5F, 7B).................................................... 11 10(9). Posterior arms of dorsal phallic sclerite slender, sinuous, and divergent (Figs 2E–2H)................... C. mammillatus - Posterior arms of dorsal phallic sclerite thick with heavily sclerotized apices (Figs 6E–6H)................... C. collaris 11(9). Subapicomesal spine I of each inferior appendage very near apex (Figs 7A–7D)............................ C. bifidus - Subapicomesal spine I conspicuously preapical, with variable distance between spine and apex of inferior appendage (Figs 1B, 2B, 5F)............................................................................................ 12 12(11). Dorsal phallic sclerite complex (Figs 1C–1E), its anterior arms well-developed and with long sclerotized rods projecting anterad (Figs 1A–1E)............................................................................ C. arotron - Dorsal phallic sclerite simple or indistinct (Figs 2C, 5H), with anterior arms reduced or absent...................... 13 13(12). Subapicomesal spines of each inferior appendage flat (Fig. 2B); dorsal phallic sclerite with anterior arm reduced, posterior arms divergent, short, and thick (Figs 2A–2D)......................................................... C. guyanensis - Subapicomesal spines circular in cross-section (Fig. 5F); phallic dorsal sclerite indistinct, without anterior arm, posterior arms fused into tube (Figs 5E–5H)...................................................................... C. ulmeri

Published as part of Rueda Martín, Paola A., Gibon, Francois-Marie & Sganga, Julieta V., 2021, New species and records of the Neotropical genus Cyrnellus (Trichoptera: Polycentropodidae) and the re-establishment of C. minimus and C. marginalis, pp. 15-29 in Zootaxa 5082 (1) on pages 27-28, DOI: 10.11646/zootaxa.5082.1.2, http://zenodo.org/record/5783094