Clay imprints of the inside of shells
The picture above shows an imprint in clay of the inside of the shell of the land snail Discus rotundatus. The shell is from a waterlogged estuarine archaeological site in Somerset, and the clay is the sediment in which the shell became buried; which filled the empty shell, and fell out of the broken shell when it dried after the shell had been separated from a bulk sample of the clay. It clearly shows the architecture of the shell, especially the highly characteristic striations.
The picture below shows a similar clay imprint from a different sample taken on the same site, this time from a bivalve, the cockle Cerastoderma edule. This clay is helpful to me, because it clearly shows that it has been inside a complete shell, whereas by the time the shells came to me for analysis, the two valves had come apart. This piece of clay also contains several smaller shells itself, of the gastropod Ventrosia ventrosa.