Scott, R. W. 1970. Paleoecology and paleontology of the Lower Cretaceous Kiowa Formation, Kansas. The University of Kansas Paleontological Contributions 52: 1-94.Original description from Scott (1970, p. 59-60):
"Shell small, subquadrate in outline, nearly equilateral, equivalved. Beak moderate size, projecting slightly beyond hinge line. Dorsal margin long, straight; dorsal-anterior broadly rounded; ventral anterior sharply rounded; ventral margin gently convex; ventral-posterior corner angular; posterior straight, sloping toward beak. Anterior umbonal ridge gently rounded; posterior umbonal ridge sharply rounded. Ornamented by thin shallow growth lines.
Dentition taxodont, otherwise unknown. Ligament external, narrow, markings unknown. Measurements of largest shell: length incomplete, 9 mm., height 7.4 mm., thickness of articulated specimen 4.5 mm."Original remarks from Scott (1970, p. 60):
"This species differs from Breviarca habita by the noncancellate ornamentation, by the less produced posterior, and by the less angular posterior umbonal ridge. The trivial name, angulata, refers to the distinctive angular ventral-posterior corner."