What is the collective noun for shells?

There isn't one widely accepted collective noun for shells.

However, here are some options you could use:

* A pile of shells (straightforward and common)

* A heap of shells

* A collection of shells

* A hoard of shells (implies a large or gathered collection)

* A scattering of shells (implies a spread out group)

Ultimately, the best option depends on the context and the specific type of shells you are referring to.