Mega-shell

Mega-shell

Observation - Mega-shell. Description: Found this odd shell in a garden (where it was obviously being used ornamentally). Seemed very large. Any idea what it once was? To give an idea of scale the lens-cap shown is about 65mm in diameter.

Found this odd shell in a garden (where it was obviously being used ornamentally). Seemed very large. Any idea what it once was?

To give an idea of scale the lens-cap shown is about 65mm in diameter.