Figs 1–3. Isalomyia irwini Stuckenberg. 1. Female head, lateral, the projecting paragular sclerite arrowed; internal recurved basal part of labium shown by dark line. 2. Complete male labium, anterior surface on right, recurved basal section at upper end; the arched form of exposed part is an artefact caused by detachment from the syntrophium which normally lies in the labial gutter and keeps the labium straight as in Fig. 1; dark line running internally over length of labium is produced by two narrow, parallel, sclerotised strips embedded in membrane of labial gutter; inset are two enlarged portions showing internal location of the strips which are closer to anterior surface basally where gutter is absent; corrugated posterior integument also shown. 3. Diagrammatic representation of form of stipital sclerites embedded in membrane under the head; they converge posteriorly and fuse.