[3] Species of this genus are very similar to those of Protaspis, but, are found in Early Devonian-aged strata of Western Europe and Podolia, Ukraine.

Cosmaspis is restricted to marine environments of Early Devonian Wyoming and possibly Utah, where it coexisted with species of Protaspis, Lampraspis, Eucyclaspis, Oreaspis and Cyrtaspidichthys.

Species of Oreaspis are found in Early Devonian marine strata of Water Canyon, Utah, and Beartooth Butte of Wyoming.

Species of Psephaspis, which are restricted to Idaho and Utah, have broad, flat, rounded and heart-shaped dorsal shields, and ornamentation similar to those of psammosteids.

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.

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.