Large Ostrich Foot.

Commonly found on sandy beaches, there have been a number of subspecies named. Suffice to say each area has its form. This is the west Cookian form. Young shells are nicely patterned, attractive and do not form the aperture lip until reaching mature size.
Older shells often have a heavy lip, nodules and become plain to rusty in appearance.
Just what old age does to us all!

Hermit crabs love old shells.