Rhiostoma sp.

Material examined.

Specimens from limestone outcrops in Ngoy Town, Ngoy District, Luang Phrabang Province (Figs 11E, 18F).

Remarks.

These specimens differ from Rhiostoma morleti, R. marioni, R. christae Thach, 2016 and R. herosae Thach & Huber in Thach, 2017 from Laos and Vietnam in having a long, descending and curved detached-whorl (proboscis-like detached-whorl), an aperture opened subventrally, and with a short and complete tubular accessory respiratory structure close to the aperture. In contrast, these four nominal species have a short to absent detached-whorl, a complete tubular or canal-like accessory respiratory structure, and an aperture opened laterally.