Type species. – Orthis delicatula Billings, 1865; by original designation; Middle Ordovician, Darriwilian; Newfoundland.
Diagnosis emended. low planoconvex; parvicostellate; small interareas with rudimentary pseudodeltidium but larger chilidium; short dental plates posterolaterally bounding small ventral muscle field; small cardinal process; bladelike socket ridges; median ridge absent but larger pseudopunctae sometimes developed along midline; distinct pustules ordered in concentric and radial rows outside muscle field.
Species included. Orthis delicatula Billings, 1865; Pelonomia ? sp. Benedetto in Benedetto & Cech, 2006; Pelonomia sulcata sp. nov.