>Dear Rich,
>Thank you very much for your valuable opinion, my "mystery shell"
>looks very much to Brotia dactylus in your image but I am not sure
>as the periostracum of the mine was removed and I don't have
>experience to the freshwater species. For your information I
>received privately another opinion for it as Brotia asperata, I will
>have the paper.
>Best regards.
>George

In my experience all freshwater Cerithioidea have strong varnishlike
olive periostracum (often covered in a peculiar smooth black crust).
Thiara, Melanopsis, Melanopsis, Pleuroceratidae... easily removed by
bleach. The shells often displays axial flames, which may not be
visible through the periostracum.
--
Andrew Grebneff
165 Evans St, Dunedin 9001, New Zealand
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Seashell, Macintosh, VW/Toyota van nut