Main text for set is below image 2 02 Patella shell. Interior of Patella vulgata shell. Length 20.2mm. Specimen chosen for clarity. Many P. vulgata are not as clearly marked or so coloured. .

Exterior layer M+3 eroded from apical area exposing interior layers. Exposed M+2 recognised by its concentric iridescent ripples (magnified in inset).

Links and references
Cohen, A.L. & Branch, G.M. 1992. Environmentally controlled variation in the structure and mineralogy of Patella granularis shells from the coast of southern Africa: implications for palaeotemperature assessments. Palaeogeography, palaeoclimatology, palaeoecology, 91: 49-57. www.whoi.edu/fileserver.do?id=163844&pt=2&p=36767

MacClintock, C. 1967. Shell structure of patelloid and bellerophontid gastropods (Mollusca). Peabody Museum of Natural History, Yale University. Bulletin 22. pdf at
www.google.co.uk/?gws_rd=ssl#q=MacClintock%2C+C.+1967.+Sh….
215 pages, may take a few minutes to download. Contents on page v.(= p.6 of pdf). To find pages on pdf add 1 to Roman numerals, and add 11 to modern numerals.