Article: A new subfamily of the Pteraspididae (Agnatha, Heterostraci) from the upper Silurian and lower Devonian of Arctic Canada

New Pteraspididae from the upper Silurian and lower Devonian of arctic Canada differ from established members of the family in possessing a single orbito-cornual plate and a pineal plate enclosed by the dorsal disc. A new subfamily of the Pteraspididae, the Anchipteraspidinae, is raised to accommodate five species of the new genera Anchipteraspis, Ulutitaspis, and Rhachiaspis. Consideration of the growth and structure of the shields of the Anchipteraspidinae indicates their close relationship to both the Cyathaspidinae and early members of the Pteraspidinae. It is proposed that the Pteraspididae were developed from the Cyathaspidinae by processes both of fusion and subdivision of the shield and that the Psammosteida developed from the Pteraspidinae by similar processes.