Rhaetavicula contorta (Portlock)

Upper Triassic, Penarth Group, Westbury Formation

Cloghfin Port, Islandmagee, Co. Antrim

field of view 150 mm across

A distinctive thin-shelled bivalve that sometimes occurs in great abundance in dark laminated mudstones near the top of the Triassic, just below the base of the Lower Jurassic Lias Group.