 They are represented by a single genus, Astraspis, including possibly two species, "A. desiderata" and "A. splendens" but their remains are fairly abundant in Ordovician sandstones of the USA (Colorado, Arizona, Oklahoma, Wyoming) and Canada (Quebec).The head armor of Astraspis is rather massive, with a series of ten gill openings lining the margin of the dorsal shield, and laterally placed eyes.The dorsal shield is ribbed by strong longitudinal crests, and the tail is covered with large, diamond-shaped scales.