A natural negative, (external mould) from a clay ironstone block, reversed to show the specimen in positive relief. A fine oxycone internal mould with some test, mainly one side and venter, with part of the other side. It shows the characteristic funnel-shaped umbilicus and sickle-shaped ribs. From West Dereham, Norfolk, England.
Size: 95 mm in diameter.
Size: 95 mm in diameter.