Named for its trough-like shape and its large size, this is the largest of New Zealand's trough shells, reaching up to 12 centimetres in length. The shell is thick and heavy, built to withstand the pounding of the surf. It lives on exposed surf beaches, burrowing deep into the sand where waves break. A large trough shell can be buried 30 centimetres down, hidden from view. The shell is white or pale grey, sometimes tinged with brown. The surface is covered in fine concentric ridges, the growth rings that mark the clam's age. A 15-year-old trough shell has 15 rings, each one representing a year of survival in the harsh surf zone. The rings are closer together in winter, when food is scarce, and further apart in summer, when the clam grows faster. Its strong, heavy shell is well adapted to survive the pounding of the surf. The weight of the shell helps anchor the clam in the sand, preventing the waves from washing it away. The shape is elongated and slightly curved, allowing the clam to burrow efficiently. The front end is rounded, the back end is pointed, and the hinge is strong. It is often found washed up on beaches after storms. The waves tear it from its burrow, tumble it in the surf, and deposit it on the high tide line. There it lies, bleached by the sun, until a beachcomber picks it up. The shell is heavy in the hand, a solid reminder of the power of the sea. Its tough, chewy flesh is less popular for eating than that of other surf clams, but it is still collected by some beachgoers. The meat must be tenderised before cooking, pounded with a mallet or soaked in a marinade. Even then, it is an acquired taste. The large trough shell is a clam for the patient, for those willing to work for their meal.