It is named from the seaside town of Penarth near Cardiff in south Wales where strata of this age are exposed in coastal cliffs southwards to Lavernock Point.

The Langport and Cotham Members, grey limestones of marine origin with associated mudstones, are recognised within the Lilstock Formation, itself named from Lilstock in west Somerset.

[2][1] The Westbury Formation is named from Westbury-on-Severn in Gloucestershire.

[3] In 1999, the discovery of an ichthyosaur from Langport Member mudstones exposed at Waterloo Bay, Larne, provided the most complete example of this in Northern Ireland.

This article about a specific stratigraphic formation in the United Kingdom is a stub.