Cross-sections of gastropods (the whitish structures) in slabs of naturally weathered dolomite in the Middle Ordovician Pogonip Group, Death Valley National Park. Called scientifically Palliseria robusta. From the westernmost exposures of an association of several world-famous geologic rock formations whose correlative age-equivalent outcrops occur in Nevada and western Utah.

Top image--courtesy the National Park Service. Second from top--photographer unknown. Third from top--photograph courtesy an individual who goes by the cyber-name urbandispute. Bottom image--photograph courtesy Steve Stern.