« Shell lengthwise rounded-oval, slightly convex, thin, transparent, shiny, smooth, white, of a dark purple near the beaks, laterally ferruginous, anteriorly subangulated, rounded posteriorly. Umbones prominent, straight, almost touching one another. Cardinal tooth blunt and very distinct. Croulin Island, between Skye and the mainland of Rossshire towards Applecross, where six specimens were found by Mr. Barlee and myself with the other species. » – J. G. Jeffreys: “Additional notices on British shells”, Annals and Magazine of Natural History vol. XX, London 1847, p.19.