Small periwinkles – forty years ago in my nature notebooks

Small Periwinkles are beautiful. Forty years ago today on 15 August 1976 I was on holiday and I was describing them in my childhood nature notebooks:

Westray has many Flat Periwinkle shells on its beaches. I can see that the Periwinkles I saw 40 years ago definitely weren’t the Flat Periwinkle; they were the wrong shape and far too small. I collect some shells and take them back to Einar. I wonder how many whorls they have?