Ralfsia verrucosa?

Ralfsia verrucosa?

Observation - Ralfsia verrucosa? - UK and Ireland. Description: This brown encrusting weed was growing in a pool just below high water neaps (upper edge of the barnacle zone) on a fairly exposed North Cornish shore. Approximately 20mm across. Can anyone point me at a reference with a key for Ralfsia found in the U.K.

This brown encrusting weed was growing in a pool just below high water neaps (upper edge of the barnacle zone) on a fairly exposed North Cornish shore. Approximately 20mm across. Can anyone point me at a reference with a key for Ralfsia found in the U.K. or NE Atlantic?