Differs by Pecten maximus (Linnaeus, 1758) by its more square ribs instead of the more flatter ribs from Pecten maximus. Both valves 16~18 ribs but flat on top which in turn are each radially grooved forming 4 ridges. This is the famous St. James shell used as a badge by the pilgrims to Compostella in N. Spain and also used in heraldy.