Decorative bowls made from striped limpet shells that I collected on the west coast of Maui during a wonderful holiday a few years ago. I think that they are black-foot opihi, a species endemic to Hawaii (only found there). Limpets live on shoreline rocks and their shells wear to fit snugly against the rock so that they can resist pounding waves. This means that the shells are irregular and may show some damage, although I have chosen the best of my shells for these pieces. The bases are silver coloured metal.
The bowl on the right has an added curiosity - an immaculatley drilled tiny hole, which was almost certainly made by another, predatory, mollusc drilling through the shell!
Left: 1 inch (2.5 cm) wide, 13/16 inch (2.0 cm) deep and just over 3/8 inch (0.95 cm) tall.
Right: just under 1 inch (2.5 cm) wide, 3/4 inch (1.9 cm) deep and 3/8 inch (0.95 cm) tall.