Fusiform and bulbous, length to 9.3 mm. Protoconch of 2 shiny, glassy brown whorls. Adult shells with 5 whorls. Sutures well defined and simple, whorls convex, smooth and shiny. Body whorl bulbous, aperture wide and rounded. Columella with 4 columellar folds. Outer lip rounded, lip edge round and smooth, strong labral lirations visible within the aperture of adult shells but missing in juvenile specimens, siphonal notch wide and flared, siphonal canal very short. Base with 3 to 8 spiral grooves. Colour varies as the shell matures, large shells with the body whorl tinged mossy green, medium size shells blue-grey, juvenile shells brown. A distinctive band of faint white lightning-shaped streaks near the centre of the body whorl.

Austromitra viridimuscus n. sp. has been confused with Austromitra analogica (REEVE, 1845) (Fig. 5), 3 syntypes, NHMUK 1966667. A. analogica is larger to 13.1 mm, with 10-14 strong axial ribs on the early whorls. In adult shells the axial ribs may become obsolete on the body whorl. This new species is variable in colour from brown, to blue-grey to mossy green on the body whorl, A. analogica has a totally different colour pattern, having a wide brown band below the suture, a central white band at the periphery of the body whorl, another wide brown band, usually the widest band, located just above the aperture line to just above the first columellar fold, another narrow white or cream coloured band from just above the first columellar fold to just below it, finally the columellar tip is brown. The lack of labral lirae in some juvenile specimens in the type lot is a common occurrence in Austromitra species.

Australia, New South Wales, Sydney area, Long Reef and the Victorian coastline. Intertidal under rocks and green algae.