"Hammer Oyster." Subequivalve, irregular, rugose; dorsal margin long, produced into a narrow wing on each side; medium portion long, narrow, waved; hinge straight, without teeth, with an elongated, conical resilifer under the small, diverging, central, umbos; ligament partly external, short; a deep byssal notch in the right valve. The pearly lining of the valves does not extend as far as the ventral margin in the adult.
Distribution: Indo-Pacific. Southern Ocean.
Remarks: The young shell is like a Pteria, but, during the growth of the animal, layers are developed from the edge of the valves, until the shell assumes the peculiar elongated form indicated by the genus name, which signifies a hammer or mallet.