The solid shell is imperforate and depressed globose. It is slate-colored or black, sometimes (especially if worn) reddish or brownish. The conic spire is short. The apex is acute, usually reddish. The sutures are linear. The five whorls are slightly convex, rapidly increasing and spirally obsoletely striate. The body whorl is usually depressed or subconcave below the suture. The base of the shell is rounded, eroded and iridescent in front of the aperture. The aperture is huge, oblique iridescent. The outer lip is rather thin, not black-margined within; but bordered by a brilliantly iridescent band; The columella is concave, obsoletely subdentate below, very broad and flattened or excavated on the face. It is composed principally of an opaque white layer which also lines the base but does not extend to the edge of the lip. The length of the shell varies between 15 mm and 26 mm. Its diameter varies between 17 mm and 24 mm.[3]
^ abDonald, Kirsten M.; Kennedy, Martyn; Spencer, Hamish G. (2005). "The phylogeny and taxonomy of austral monodontine topshells (Mollusca: Gastropoda: Trochidae), inferred from DNA sequences☆". Molecular Phylogenetics and Evolution. 37 (2): 474–483. doi:10.1016/j.ympev.2005.04.011.
^Spencer H. G., Marshall B. A. & Waters J. M. (2009). "Systematics and phylogeny of a new cryptic species of Diloma Philippi (Mollusca: Gastropoda: Trochidae) from a novel habitat, the bull kelp holdfast communities of southern New Zealand". Invertebrate Systematics23: 19-25. doi:10.1071/IS08030. PDF.
Williams S.T., Karube S. & Ozawa T. (2008) Molecular systematics of Vetigastropoda: Trochidae, Turbinidae and Trochoidea redefined. Zoologica Scripta 37: 483–506
