Figure 15: Sections of Involutina liassica (Jones). Middle Lias, from Arzo, Ticino, Southern Switzerland. Transparent light micrographs. Involutina exhibits a lamellar-perforate, planispiral-evolute, dimorphic shell with a spherical megalosphere followed by a tubular chamber cavity without septa. Lateral walls ornamented by protuberant piles between coarse pores. Double arrow: shell axis.
a: axial section; e: equatorial section; o: oblique section; oc: oblique-centered section; ta: tangential section; tr: transverse section.