I didn't know that Balea heydeni had become Balea sarsii, but it looks like it is just a name change which is not yet generally adopted in this country, so it should be Ok to continue to use Balea heydeni.
Up to 2005 Balea perversa was the only species recognised in this country. It was then recognised that Balea heydeni was here so in effect B.Perversa was split into two, but retaining the name B.perversa, now with a different meaning, and introducing a new name for this country of B.heydeni. This makes older records for B.perversa inaccurate in that they now refer to an aggregate. Recorder 6 should be pointing the older records to the Balea perversa/heydeni aggregate. New records should be input by using the preferred mollusc list which has the split and the aggregate.
As I understand it. it is B.heydeni which is thought to be the most common species in this country and therefore that most older records probably refer to this rather than to B.perversa under which it was orgiginally recorded, but the only safe thing to do without specimens is to consider them as the aggregate.
The Conchological Society, Journal of Conchology contains a detailed paper explaining the difference between the two species.
Journal of Concholgy Vol 30 Part 2, November 2006, Gittenberger E, Preeece RC & Ripken ThEJ - Balea heydeni - an overlooked but widely distributed Europena species.
Also the AIDGAP key Land Snails in the British Isles (Second edition 2008) covers the two species.
Mike Weideli