Hey, here's a quick unfinished scallop shell ulu I made the other day to see how well it would work.  I have seen ones made from clam shells before and having lots of these scallops on the beaches here I thought I'd give it a go.  All in all it works quite well and diced my carrot just fine!

Looks really nice!

Have you somehow sharpened the shell or was it sharp enough by nature?

Very cool, I've read of some west coast tribes using shells to make arrowheads before. Its not often you see someone actually putting it to practical use. 

  They are sharp enough when you find them, but you can just sharpen them up after using them a while by grinding, same way you would a steel ulu, sandpaper works great for it or just a sandstone.
  You could make a lot of variations of that, for example you could split a stick and lash the two ends together rather than gouging it out then tie it same as this one.  You could also simply  make a hole big enough for the hinge at the bottom of the shell and use pitch to secure it in the handle.  I would think you could even use wooden pegs as you can with a slate ulu.

that's pretty good i like it.

If that's a scallop shell, why isn't it scalloped? All the ones I've seen were.

All the scallop shells I've seen are ribbed or ridged, not smooth, and the edge isn't a continuous curve; it's sort of like a sine wave. It would give carrots a fancy crinkle cut.

How hard are these shells? You can cut soft material but could you make an adze to chip wood?