Hello Francisco, you are looking for studies conducted at the European scale, correct? Here's one I am aware of, focusing on urbanization and land snail diversity in urban areas of central Europe:

Horsák M, Lososová Z, Čejka T, Juřičková L, Chytrý M. Diversity and Biotic Homogenization of Urban Land-Snail Faunas in Relation to Habitat Types and Macroclimate in 32 Central European Cities. Shaw P, ed. PLoS ONE. 2013;8(8):e71783. doi:10.1371/journal.pone.0071783.

I hope it may be of use, best wishes

Danilo

Grazie Danilo ! My main interest was on overall patterns of species diversity across Europe...

Dear Fransisco,

I remember there was a study on the same topic in Germany several years ago (more than 10). It was conducted by a research team at Dr. Johann G. Goldammer's office (Freiburg, Germany). You can get in touch with them. I do not know whether they have published it somewhere.

with my best regards,

Ertugrul.

I think we need more detail: diversity at what scale? you will find lists by country in Fauna Europaea. I have lots of published work on the diversity of particular sites across C. & E. Europe and in Britain, and the turnover in species among them. If you contact me with  the sort of info you want, I can send you stuff. I am attaching a review article with a number of leads, and an earlier, less critical survey.

 What kind of diversity? Variation in richness at various scales, or differences among regions/areas/plots in taxonomic composition.

For some broad overviews, concerning latitudinal gradients and the nestedness of faunas,, any work by Bernhard Hausdorf and colleagues is a good starting point.

Size of area is crucial. Mediterranean (esp. E. Mediterranean) countries have very rich faunas with very high endemism rates, but at the level of small sites (say 1 ha or less)  sites in the north are often the richest.

Cheers, Robert Cameron.

PS. I will be in Lisbon 1 and 2 May for the Portuguese Malacological Conference

Thank you all for your useful comments. My main interest would be southwestern Europe, the Iberian peninsula in particular.