Shell-form intermediate between costate and non-costate.
1: protoconch of three whorls; as always, lacks any sculpture.
2-2: three whorls after protoconch with strong costae; produced in summer when optimum growth conditions (Wigham, 1975b).
3: glossy and translucent body-whorl lacking costae; produced in winter/early spring when stress of cold and wave-exposure prevented development of costae. (Wigham, 1975b).