Cosmoptychius

Cosmoptychius is an extinct genus of freshwater and estuarine ray-finned fish that lived during the Mississippian epoch. It contains a single species, C. striatus from the Visean of Scotland. It has a wide stratigraphic range in the Wardie Shale, with many specimens known.

Initially classified as either a palaeonisciform (a now-paraphyletic group of basal actinopterygians) or the earliest stem-group neopterygian, it is now generally considered a stem-group actinopteran.