Types: MALAYSIA: State of Sabah, Pensiangan District, Sapulut area. Limestone – Batu Sanaron (4°42 ′ N, 116°36 ′ E). Collected by T.- S. Liew, M. Schilthuizen, and S. Chiba. Date: 25.vi.2005, holotype, BOR/MOL 4277, Figure 2C; ten paratypes, five in BMNH 20080627 and five in SP 13059.

Etymology: This species is named interior for its distribution range in the interior of Sabah.

Material examined: SABAH – Sapulut: BOR/MOL 921, Sanaron cave, 450 m alt., vii.2000; BOR/MOL 929, Batu Temurung, ii.2001; BOR/MOL 939, Sanaron cave, vii.2000; BOR/MOL 969, Batu Sinobang, 450 m alt., ii.2001; BOR/MOL 1137, Batu Tinagas, 450 m alt., vii.2000; BOR/MOL 4305, Sanaron cave, vi.2005; BOR/MOL 4332, Batu Punggul, vi.2005; JJ 1304, Pun Batu, ix.1986; JJ 1974, Batu Punggul, v.1987; JJ 5627, Batu Sinobang, 1997; JJ 7546, Batu Pungiton, vii.2000; JJ 7626, Batu Tinagas, vii.2000; JJ 7662, Sanaron cave, vii.2000; JJ 7726, Kg. Labang, vii.2000; JJ 7995, Batu Sinobang, ii.2001; JJ 8038, Batu Temurung, ii.2001; JJ 8069, Sanaron cave, ii.2001.

Diagnostic characteristics: Shell suture depressed with widely placed spiral grooves.

Description: Shell (Figs 2C, 3A): medium-sized, rather thin, brownish, moderately elevated, outer whorls rounded. Periphery rounded, suture depressed. Above the periphery, shell shiny with widely placed spiral grooves, c. 4–5 per mm, numerous fine spiral striae in between grooves. Below the periphery, shell has fine, densely placed spiral grooves. Height up to 11.4 mm; width up to 19.7 mm; diameter of the first three whorls 1.0–1.1, 0.9–1.0, and 1.7–1.8 mm, respectively; number of whorls up to five; height aperture up to 8.2 mm; width aperture up to 10.7 mm. Genitalia (Fig. 7H): maximum length from genital opening to the end of dart-sac (before the visible gland tubules) up to 13 mm. The penis, dart-sac, and vagina with thick muscular walls. P, V, GO, BC, and DS arranged around the short genital atrium, limited space between the openings of each of the genital structures. The BC is short, about one-third of total DS length. ANIMAL (Figs 4B, 8E): black bands on either side of the tentacles, which are separated by a white band that occupies the space between the eye tentacles. Black bands extend downward to just below the eye tentacles and backward from the umbilicus region to the end of the tail, downward to the edge of the foot. The mantle is black and covered by crowded tiny brighter spots and followed by regularly spaced radial black bands at the last half whorl.

Distribution and habitat: Primary forest. Sabah: Sapulut area (Fig. 5B).