Millardaspis n. gen.

Type species. Millardaspis milsteadi n. sp., from the Garden City Formation (Floian; Tulean; Heckethornia hyndeae Zone), Hillyard Canyon, Bear River Range, Franklin County, southeastern Idaho, USA.

Other species. Millardaspis knoxi n. sp., Fillmore Formation (Tulean; Panisaspis sevierensis Zone), western Utah,.

Etymology. From Millard County, and Greek aspis, shield. Gender is feminine.

Diagnosis. Cranidium strongly (sag.) and moderately (tr.) vaulted, with low glabellar inflation; axial furrows relatively wide and shallow; palpebral lobe broad; dorsal tuberculate sculpture dense all over exoskeleton (pygidia partially effaced in large specimens), granulose to tuberculate; pygidial pleural ribs laterally compressed and bladelike; pygidial pleural spines with strong ventral curvature.

Discussion. Millardaspis is proposed for a pair of species with highly distinctive pygidia which feature laterally compressed pygidial pleural ribs and spines that are strongly down-curved. This results in a plan view shape completely unlike any other member of the overall clade, all of which have rounded ribs and spines which splay laterally in plan view.