A taxonomic and nomenclatural history of Codriophorus aquaticus (Schrad.) Bednarek-Ochyra & Ochyra [Trichostomum aquaticum (Brid.) ex Schrad.; Racomitrium aquaticum (Schrad.) Brid.] is presented. A specimen from Llanberis in Britain, preserved in the Dillenian herbarium in OXF and illustrated in Historia muscorum of 1741, is selected as lectotype of this species name. The lectotype specimen is described and illustrated and it represents the typical phenotype of the species that is characterized by having entirely unistratose leaf lamina; entire leaf margins including the apex; presence of a basal marginal border of up to 15 transparent cells with straight walls; and very stout, thick, and broad costae with 10–13 enlarged adaxial epidermal cells in the proximal part.