L. solenoides. The Solen-like Lutraria.
Species oblong, sub-cylindrical, very gaping, two very strong cardinal teeth; the spoonlike cavity of the ligament vertical.
L. compressa. The compressed Lutraria.
Species oval or orbicular, almost equilateral, very compressed, little gaping; hinge similar; internal ligament inserted in the pit of a vertical spoonlike cavity; two distinct tubes, without longitudinal striæ.
L. rugosa. The rugged Lutraria.
Species ovate, closed at both ends; striæ from the summit to the base.
L. elliptica. The oval Lutraria.
Oblong oval, nearly smooth, having a few concentric striæ, and some diagonal striæ at the ends of the valves; colour yellow or greenish brown; inside white.
2. Mactra. The Kneading-trough. Thirty-three species.
The name given to this genus was derived from the Greek word μακτρα, from its resemblance to a trough used for kneading bread.