Because of these two traits, species of this genus were originally described as being North American psammosteids closely related to Drepanaspis by Orvig. Denison then redescribed them as being pteraspidids closely related to Protaspis, noting that the overall anatomy is that of a typical pteraspidid. Denison also notes that Psephaspis is the youngest genus of pteraspidid, as specimens of P. idahoensis are found in Middle Devonian-aged strata of Lemhi County, Idaho, which are younger than the latest strata other pteraspidids are found in. Rodenaspis This genus was established by Blieck in 1984 when he elevated Protaspis (Protaspis) brevispina into a separate genus, noting its cornual processes are distinct from Protaspis. Tuberculaspis Tuberculaspis is known from Early Devonian marine strata of Nevada, where it coexisted sympatrically with the protopteraspidid Lamiaspis, and fellow protaspid Pirumaspis in a shallow-water marine environment. It is named for tubercule-like growths that decorate the borders of its dorsal shield. Xylaspis This Spitzbergen protaspid was originally named Spitsbergaspis, but that name was discovered to be preoccupied by an Ordovician trilobite. It is similar in form and related to Zascinaspis and Woodfjordaspis. Zascinaspis Species of Zascinaspis are found in Early Devonian marine strata of Spitzbergen, and are similar in form to Xylaspis, Woodfjordaspis and Gigantaspis, the former two genera being closely related. Woodfjordaspis Woodfjordaspis is known from an incomplete, partially articulated armor found in early Devonian-aged marine strata of Spitzbergen. It is similar in form and is closely related to Zascinaspis and Xylaspis. Pirumaspis This protaspid is from the Sevy Dolomite Fauna of Late Emsian-aged marine strata in Nevada, where it coexisted sympatrically with Tuberculaspis, and the protopteraspidid Lamiaspis. References Palaeos Vertebrates entry on order Pteraspidiformes Pteraspidiformes Devonian jawless fish Early Devonian fish Prehistoric jawless fish families Early Devonian first appearances Early Devonian extinctions