Special Papers in Palaeontology, published by The Palaeontological Association, is a series of substantial separate works conforming to the style of the Palaeontology journal. This issue investigates the thelodonts and putative chondrichthyans from rocks of upper Llandovery (Lower Silurian) to Lochkovian (Lower Devonian), and from Baillie-Hamilton and Cornwallis islands, Arctic Canada. It presents new anatomical information which will allow greater precision in future phylogenetic studies of thelodonts and related vertebrates.