Euspira napus is a species of predatory sea snail, a marine gastropod mollusk in the family Naticidae, the moon snails.
The diameter of the shell varies between 30 mm and 40 mm.
The shell is rounded, solid, and smooth, with a low spire. Its aperture is semi-circular, bordered by a thin outer lip, while the base features a distinct yet narrow umbilicus and a slightly thickened edge on the inner lip. The surface sculpture consists of fine, closely set growth lines. The living animal has a horny operculum.
The shell is white, with a dull brown periostracum (a thin, skin-like outer covering), typically displaying a pattern of fine spiral lines.
This species is endemic to South Africa and occurs off Port Alfred and the Agulhas Bank (False Bay to western Transkei) at depths between 50 m and 210 m.