Late adult with high conoid shell, GS5f, on Laminaria frond.
Aperture outline a broad oval, 14mm X 10.5mm. Although a large adult, the shell remains quite thin and translucent showing the viscera, and it retains the longitudinal dark chestnut band on the pedal-retractor muscle, as on juveniles. This suggests that these features are related to frond dwelling rather than maturity. The causal factor may be light compared to those with thicker shells in the dark of holdfasts, as suggested by Graham & Fretter (1947), or diet; those on fronds graze the brown frond surface while those in holdfasts consume the pale core of the stipe.
The blue rays on the juvenile growth continue on the adult growth almost all of the way to the posterior edge, but have become faint shadowy grey lines on the narrow band of newest growth at the rim. There are very small fragments of blue at the anterior, but it is exceptional in Britain for anterior blue rays to be well developed like those in Norway.

Concise
Part 1, SHELL FORMS: 02 Patella pellucida. Growth Stage 2 (GS2). July 2012. Littoral. North Yorkshire, England. © P. Lightfoot.
Part 2, BODY & ANATOMY: 03 Patella pellucida. Growth Stage 3 (GS3). 2009. Sublittoral, Farne Islands, Northumberland, England. © P.Lightfoot.
Part, 3 HABITS & ECOLOGY: 04 Patella pellucida. Length 4.6mm. Growth Stage 3 (GS3). September 2016. Yorkshire, England. © P.Lightfoot.