Mesembrina Meigen, 1826: 10. Type species: Musca meridiana Linnaeus, 1758.
Diagnosis. Colouration metallic black; gena and parafacial with dense golden pruinosity; body with dense ground setulosity; basal third of wing and calypters notably yellow (or blackish in M. nigribasis from Costa Rica). Vibrissa developed, although sometimes confused with the developed subvibrissals. Female with proclinate fronto-orbital seta; parafrons densely setulose along its whole length; interfrontal seta absent; frontal vitta densely setulose on upper half or along its whole length. Presutural acrostichals developed or not; 3 postsutural setae. Dorsocentrals 1-3 + 4-5 (0+ 2 in M. nigribasis). Postsutural intra-alars 2; intrapostalar absent. Notopleurals 2-3 (usually 2 notopleurals but some species with an additional seta posteriorly). Prosternum bare. Anterior katepisternal absent or present. Meron and katepimeron bare. Posterior spiracle bare on posterior margin. Suprasquamal ridge bare. Scutellum half-moon shaped. Wing with the veins bare; costal vein setulose ventrally until Sc; Rs node and R 4 + 5 bare dorsally and ventrally; M bent forward towards R 4 + 5. Lower calypter enlarged posteriorly, extending under base of scutellum. Subcostal sclerite bare. Mid tibia with an anterodorsal submedian seta. Calcar strong.
Comments. Recently, M. nigribasis Kuchta & Savage was described from Costa Rica (referred to as Mesembrina sp. 1 in the cladistic analysis of Nihei and de Carvalho 2007 a). The Holarctic Region was probably the ancestral area of this genus, and the Neotropical and Oriental occurrences are due to subsequent expansion of distribution range followed by local speciations.
Distribution (13 species). Nearctic, Neotropical, Oriental, Palaearctic.
References. Nearctic species: Huckett (1965), Kuchta & Savage (2008); Oriental: Emden (1965), Xue and Chao (1998), Kuchta & Savage (2008); Palaearctic: Hennig (1963 b), Peris and Llorente (1963), Zimin and Elberg (1988), Xue and Chao (1998), Gregor et al. (2002), Shinonaga (2003), Kuchta & Savage (2008); Neotropical: Kuchta & Savage (2008).