A small extinct order of inarticulate brachiopods that ranges in age from Early Cambrian to Middle Ordovician. The shell is chitinophosphatic in composition, and its outline is circular or elliptical. The ventral (pedicle) valve is more convex than the dorsal (brachial) valve. The pedicle was absent or emerged between the valves. The ventral valve has a flattened posterior area (pseudointerarea) that is divided by a triangular notch which is closed to a variable extent by a plate (homeodeltidium). Comparable, but not as extensive, structures occur at the posterior end of the dorsal (brachial) valve. The muscle scars are unusual compared to other inarticulates, and form narrow triangular tracks radiating from the posterior extremity of each valve (see illustration). Except for their shell composition and lack of articulation, the Paterinida resemble articulate brachiopods. Members were presumably epifaunal and sessile.