Arca gibbosa — « Shell rotundately oval, very gibbous, equivalve, sides rather angulated, rounded beneath, anterior side shorter ; white, covered with a brown epidermis ; radiately ribbed, ribs six or seven and twenty in number, round, narrow, slightly nodulous ; ligamentary area middling. » – L.A. Reeve: Conch. iconica vol. II, plate 4 via BHL.