New material of the Madagascan vermileonid Isalomyia irwini Stuckenberg, 2002 enables a more complete description to be given. This species has exceptional apomorphies in the structure of its head and proboscis; the antennae also are highly modified, and share unique synapomorphies with an Omani species previously named Lampromyia umbraticola Stuckenberg & Fisher, 1999. A reassessment of relationships suggests that irwini and umbraticola are sister-groups. Grounds for the original inclusion of umbraticola in the genus Lampromyia Macquart, 1835 are now known to be invalid, and a new genus, Alhajarmyia, is erected for this species. Biogeographical implications of the relationship between these Arabian and Madagascan taxa are discussed. Aerial transport between Madagascar and East Africa, assisted by intermediate islands, could have occurred, and an East African centre of an ancestral form seems plausible.