The type species of the genera Idoceras Burckhardt and Subnebrodites Spath are clarified in order to preserve the current universal usage of the Planula Zone in the Upper Oxfordian and the Balderus Zone in the Lower Kimmeridgian of the Submediterranean Province. To protect both zones, the identification of Ammonites planula Hehl in Zieten, 1830 in 1830–1833, is investigated and found to be a nomen nudum.