Cyclophorus amoenus (Pfeiffer, 1854) Fig. 6C

Cyclostoma (Cyclophorus) amoenum Pfeiffer, 1854[1852]: 62. Type locality: unknown.

Cyclophorus amoenus: Nantarat et al. 2014a: 4, 5, fig. 3a, b. Nantarat et al. 2014b: 103, table 1, fig. 1b. Do and Do 2019: 6, 7, table 1, figs 1.2, 13b, c.

Material examined.

Locality no. 10: CUMZ-CM053 (21 shells), CUMZ-CM054 (1 shell; Fig. 6C). Locality no. 7: CUMZ-CM0110 (1 shell). Locality no. 11: CUMZ-CM071 (2 shells). The empty shells were collected from the ground among leaf litter.

Distribution.

Cambodia and Thailand (Nantarat et al. 2014b). The distribution in Vietnam is doubtful (Do and Do 2019).

Remarks.

Cyclophorus is the genus encompassing highly variable shell morphology of both inter- and intraspecific entities. The demarcation among different species is poorly understood. Thus, both intensive and thorough revision and redescription require more effective taxonomic characters, e.g., morphometric analysis of large series of specimens and perhaps molecular phylogeny to clarify the exact species boundaries (see Nantarat et al. 2019).

This species was described from an unknown type locality. Later, the type specimens were examined and illustrated (Nantarat et al. 2014a) and then subsequently reported from central Thailand (Nantarat et al. 2014b). Do and Do (2019) reported this species from central and southern Vietnam, but it needs revision and confirmation by more studies. The distinguishing characters of this species are a less expanded apertural lip, thickened with multiple layers and with a highly variable colour pattern.