Phylum: Rhodophyta   Family: Palmariaceae

Palmaria palmata  (Linnaeus) Weber & Mohr, 1805

Dulse

Epiphytic on larger seaweeds and also on rocks to a depth of 20 metres. Reddish brown, flattened fronds, simple or sparingly branched, often with secondary stalked fronds

References: 
Fish & Fish (2011) - A Student's Guide to the Seashore;
Bunker, et al - Seaweeds of Britain and Ireland