A lovely collection of nerite seashells under a glass dome. All the different patterns and colours are totally natural. Most of these, if not all, are actually one highly variable species of nerite!
I took a photo before securing the dome in place with a water-soluble glue, so that if you wish to remove the dome you can by gradually moistening the base of the glass. It is hard to take photos with the reflections from the photographic lights but one's eye sees much better and compensates for such reflections in person.
1 inch (2.5 cm) diameter at base, 1 3/4 inches (4.4 cm) tall.