The ultrastructure of ribbon-like deposits over the thecae in Orthograptus gracilis Roemer
Adam Urbanek and Grażyna Mierzejewska
Acta Palaeontologica Polonica 23 (4), 1978: 637-642
The periderm of Orthograptus gracilis has bee studied with an electron microscope (TEM and SEM). Four components have been recognized within the thecal wall: 1. endocortex, 2. fusellar layer, 3. cortex and so-called 4. taeniocortex. Taeniocortex covering the outer surface of the thecal wall consists of ribbon or sometimes roller-like elements and is produced of a peculiar material. The data obtained do not confirm Andres' belief that ribbons are made of cortical material and that entire cortex was produced by deposition of ribbon-like units.
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