This paper includes descriptions of Thelodontid scales (gen. et sp.indet.) and Acanthodian jaw-bones (Atopacanthus sp.) from the Devonian of Spitsbergen, and of a Petalichthyid Arthrodire, Ellopetalichthys scheii (Kiær), from the Devonian of Ellesmere Land. Remarks are also given on the endoskeletal hard tissues in some representatives of the Osteostraci (Benneviaspis), the Brachythoracid Arthrodire (Dunkleosteus, etc.) and the Paleozoic Elasmobranchs (Tamiobatis, Coelosteus). The microstructure of the Palaeomylus tooth plates is dealt with, and the Ptyctodontid affinities of certain Ichthyodorulites from the Devonian of North America (Eczematolepis, Gamphacanthus) are discussed.