Fig. 5 in The morphology and fine structure of the Ordovician Cephalodiscus-like genus Melanostrophus

Fig. 5. Melanostrophus fokini Öpik, 1930; Upper Ordovician (Kukruse Stage, C β), Ubja (Estonia); ZPAL Pb 6/1. SEM micrographs. Graptolite pattern of 2 tube ultrastructure. A. Broken tube wall showing layered ectocortex and fusellar layer. B. Parallel bundles of cortical fibrils covering the fusellar layer. C. Fuselli arrangement; note the oblique suture. D. Details of fusellar fabric. Abbreviations: b, bundle of cortical fibrils; cf, cortical fibril; ec, ectocortical layer; f, fusellar layer; o, oblique fusellar suture; p, pits.