Identify "football" shell

[Uncle Jim]

On a beach at the top of the Sea of Cortez, we find a small, pink shell that is shaped very much like a football.  It is about 1/2 inch long, and rounded at both ends.  It has an opening in the middle of one side, with both sides of the shell folding into the opening.

Along the other side, there are two rows of raised lighter-colored dots, which resemble the lacing on a tiny football.

I cannot find a picture of the thing anywhere on the internet.  Can anyone identify it for me?

Thanks,

Uncle Jim