 The outer lip is thin, forming at its upper and internal part a sort of small canal at its union with the left lip.The columella is almost straight, subverrucose, and of a reddish yellow.The shell is dull brown with fine ridges along the spirals and a papery outer layer that peels off when dead, but in life is usually encrusted by the commensal bryozoan "Alcyonidium nodosum" which gives a slightly nodular velvety appearance in purplish to orangy browns Easily confused in the field with "B. pubescens", which does not reach the same maximum size.