Shell about as high as wide.
Umbilicus ?

Does the shell have an umbilicus? (The umbilicus is the cavity surrounding the axis, opening at the base of the shell.)

The adult shell of some species has the umbilicus completely sealed by the lip of the mouth – BEWARE: juveniles may still show signs of the umbilicus.

Click on the image below which has an umbilicus like your specimen.

No umbilicus