Small shells to 30 mm. Equivalve. Subequilateral. Outline subrectangular; posterior area distinct; median sinus weak; byssal gape very narrow. Dorsal area flat with a vertically striate ligament restricted to a triangular area between the beaks i.e. amphidetic. Sculpture of riblets, often nodulose or scabrous. Hinge with a continuous series of small ± vertical teeth. Adductor scars with slight myophoric ridges.