The genus Circeis St-Joseph was based upon C. armoricana St-Joseph (1894), but Caullery & Mesnil (1897) suggested that the latter is a mere variety of Spirorbis spirillum (L.), which Chamberlin (1919) therefore regarded as the type of the genus. These two species are indeed closely related to each other, but distinguished by the sculpturing of the collar setae (Knight-Jones, Knight-Jones & Al-Ogily, 1975). They belong to a genus which is very distinct from Spirorbis, as was pointed out by Knight-Jones, Knight-Jones & Kawahara (1975), who regarded C. armoricana as the type species.