The shell is roughly oval, chalky white with patches of purple and brown. Solid and variable in shape and reaches 80mm long. The rims have extended razor sharp extensions. There is a row of small beads (chromata)running part way round the edge of the shell, on either side of the hinge.

Mid intertidal of sheltered rocky shores and mudflats of northern half of North Island.

Filter feeder.

Once abundant throughout Northland, it has been replaced in many area by the more aggressive colonizer, the Pacific Oyster.
Legally Rock oysters cannot be opened when attached to the substrate they grew on and the catch limit is 250 per person per day, there is no size limit.

NZ Coastal Marine Invertebrates; Vol 1