Mellita isometra Harold & Telford 1990
Family: Mellitidae	Order: Clypeasteroida
Locality: USA, South Carolina, Atlantic	Dimensions: 55 x 57 x 7 mm (left) 60 x 66 x 7,3 mm (right)

According to the sellers information both specimen come from South Carolina and are thus with a high probability Mellita isometra.