A redescription is given for the species of the genus Bittium Gray, 1847 which is one of the most abundant components of the zoobenthos on rocky shores of the Azores. The species has been confused by almost all authors with the European species B. reticulatum (da Costa, 1778) or B. latreillii (Payraudeau, 1826) but differs enough to be considered a species endemic to the archipelago. It is proposed to use for this species the binomen Bittium nanum (Mayer, 1864), a forgotten but nomenclaturally valid name based on fossils of a terrace of Pleistocene age in Prainha, Island of Santa Maria. This name (first introduced in the binomen Cerithiopsis nana Mayer, 1864) is a primary homonym of Cerithiopsis tubercularis var. nana Jeffreys, 1867, which should be renamed or better described anew.