The ACAVIDAE are a family from the eastern and central Indian Ocean. In Sri Lanka we have the genus Acavus with a few species and the genus Oospira with only one species: the rare waltoni. Stylodonta live in the Seychelles and there are only two species. The rest lives in Madagascar, where there is an explosion of different genera and species.
Before, the family contained the present CLAVATORIDAE as a genus. Now once more considered a family on its own. Some species become particularly large: especially the Helicophanta with the giant recently discovered Helicophanta gargantua.
The genus Ampelita has many species in Madagascar and is colorful. Most Acavids live in native jungle and are hard to find.

For a list of genera and species:
http://molluscabase.org/aphia.php?p=taxdetails&id=871059

The literature:
2002 Poppe, Groh & Charles
A Conchological Iconography. Family ACAVIDAE, excluding Ampelita.

1993 Fischer-Piette, Blanc, Blanc & Salvat
Faune de Madagascar. 80. Gastropodes Terrestres.

1994 Fischer-Piette, Blanc, Blanc & Salvat
Faune de Madagascar. 80. Gastropodes Terrestres Pulmonés.