Key to Males of Mesoleptobasis

1. Costal side of FW pt shorter than basal side, its posterior margin strongly convex (Fig. 10 a); prothoracic projections in anterior view with no common stem, acuminate apices directed laterally (Fig. 4 a); attenuate cercus dorsally with a membranous central area (Fig. 17 a); genital ligula in ectal view with distal margin transverse and lateral sub-apical deep emarginations (Fig. 14 a); Amazonian region of Peru (Fig. 21) ................................................. M. acuminata

1'. Costal side of FW pt longer than basal side, its posterior margin slightly convex (Figs. 10 b, 11a–c); prothoracic projections in anterior view with a common stem, apices directed dorso-laterally (Fig. 4 c) or laterally (Figs. 4 b, d, e); cercus dorsally lacking a membranous area (Figs. 17 b–e, 19); genital ligula in ectal view with distal margin deeply bifid and lacking lateral emarginations (Figs. 14 b–e) ................................................................................................ 2

2. Prothoracic projections in anterior view with apices directed dorso-laterally (Fig. 4 c); CuA ending four cells distal to vein descending from subnodus (Fig. 11 a); posterior margin of S10 recessed and with a medio-dorsal emargination, lacking postero-lateral processes (Fig. 17 c); cercus strongly arched, curled over itself with tip directed antero-ventrally (Figs. 17 c, 18c); paraproct robust and basally as high as half of S10 height in lateral view (Fig. 18 c); genital ligula in lateral view with basal lobe low and dorsal margin of lateral lobe denticulate (Fig. 15 c); Guyana and Saramacca and Marowijne Districts of Surinam (Fig. 21) ............................................................. M. cyanolineata

2'. Prothoracic projections in anterior view with apices directed laterally (Figs. 4 b, d, e); CuA ending two cells proximal to two cells distally to vein descending from subnodus (Figs. 10 b, 11b, c); posterior margin of S10 projected medio-dorsally, with a pair of postero-lateral small lobe-like processes (Figs. 17 b, d, e, 19a–c); cercus smoothly curved, with tip directed postero-ventrally (Figs. 17 b, d, e); paraproct slender and basally narrower than half of S10 height in lateral view (Figs. 18 b, d, e); genital ligula in lateral view with basal lobe long, sclerotized, and pointed, and dorsal margin of lateral lobe with a single spine (Figs. 15 b, d, e) ................................................................. 3

3. Cercus oblong, longer than wide, and usually armed at tip with a small externally recurved tooth (Figs. 17 b, 19a); Amazonas and Rondônia States in Brazil (Fig. 21) .................................................................................... M. cantralli

3'. Cercus approximately semicircular, about as long as wide, lacking a small externally recurved tooth at tip (Figs. 17 d, e, 19b–e) ............................................................................................................................................... 4

4. Base of paraproct with a thumb-like tubercle (Fig. 18 d); FW CuA ending one or two cells proximal to vein descending from subnodus (Fig. 11 b); abdomen longer: 37–40 mm (Fig. 20 a); Para District in Surinam and Amazonas State in Brazil (Fig. 21) ........................................................................................................................................ M. elongata

4'. Base of paraproct slightly convex, lacking a thumb-like tubercle (Fig. 18 e); FW CuA ending at or one or two cells distal to subnodus (Fig. 11 c); abdomen shorter: 31–33 mm (Fig. 20 b); Amazonas State in Venezuela and Amazonas and Rondônia States in Brazil (Fig. 21) ................................................................................................ M. incus