Article: Shell structure of the Devonian retziid brachiopod Plectospira ferita
Gertruda Biernat and Andrzej Baliński
Electron microscope studies of Plectospira ferita (von Buch) show the presence of two inorganic layers, primary and secondary, as well as a third, outermost one interpreted here as a periostracum. This is the first time a periostracum has been recognized in the fossil state. The structure of the periostracum of P. ferita is described and a comparison is made with periostraca of living brachiopods. The micro-ornamentation of the shell of P. ferita is described; pits and tubercles occurring on the surface of the primary layer are considered in detail.