MATERIAL AND METHODS
The specimens referred to herein are deposited in the Zoological Reference Collection (ZRC) of the Raffles Museum of Biodiversity Research (RMBR) at the National University of Singapore, where they have been assigned catalogue numbers with the prefix ZRC. The following abbreviations are used: SH (shell height) refers to the distance from the apex to the lowest part of the basal side of the peristome; SW (shell width) refers to the widest part of the body whorl (periphery) perpendicular to the coiling axis. All measurements are in millimetres (mm).