In January 1990 the Colin Harper collection of shells in pottery and porcelain, also glass, books, watercolours & prints was auctioned via Phillips in London. Ad Hovestadt kindly lend me the catalogue of this auction, in which I found one item with land shells [1: item 68].
Both snails are clearly Helix-like species, but their color pattern is a personal interpretation of the anonymous artist who designed these ceramics.
 The Colin Harper collection of shells in pottery & porcelain, also glass, books, watercolours & prints, 24 and 25 January 1990. Phillips, London: 134 pp.