The clausiliid snail Papillifera papillaris is not native to Turkey. Its homeland is believed to be the Italian Peninsula and the nearby islands, including Corsica and Sicily. The species has been inadvertently introduced to many other locations by humans possibly on marble and marble objects. In the AMG Newsletter No. 9, I have a note on the occurrence of P. papillaris in Istanbul.
These snails naturally live on calcerous rocks. Hence their propensity to be transported on marble and limestone. The species gets its name from the more or less regularly spaced white protuberances along its sutures. The shell in the picture, from Yedikule, a Byzantine-Ottoman fort in Istanbul, was 12.9 mm long.
Update posted 21 August 2008: See this post about the discovery of this species in the UK.