Millardaspis, E.B & Adrain & Karim, 2018

E. B, Neo, Adrain, Jonathan M. & Karim, Talia S., 2018, The pliomerid trilobite Ibexaspis and related new genera, with species from the Early Ordovician (Floian; Tulean, Blackhillsian) of the Great Basin, western USA, Zootaxa 4525 (1), pp. 1-152 : 37

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.