Ringicula opima

Ringicula opima nov. spec.

(Figures 31–32)

Type material. Holotype RGM 961.757 (Type locality), paratype RGM 961.756 (Roxas), paratype RGM 961.853 (Type locality).

Other material. Roxas (12) RGM 961.829, Tiep2 (35) RGM 961.835, Tiep3 (5) RGM 961.836, Tiep4 (1) RGM 961.837, Tiep5 (21) RGM 961.838.

Type locality. Tiep2.

Derivatio nominis. Plump, adjective. Named after the thick, swollen callus of the aperture.

Diagnosis. Shell moderately large; H 3.92 mm, W 2.57 mm; protoconch slightly elevated, 1.1 whorl, DP 0.22– 0.24 mm; nucleus moderately small, DN 0.10–0.12 mm; teleoconch with distinct grooves and subsutural ridge; aperture narrow; outer lip callused, smooth, projecting beyond columella; inner lip callused, with one lamella; columella with two folds.

Description. Shell moderately elevated. Largest specimen has a total of 5.3 whorls, including a protoconch of 1.1 whorl. Protoconch small, smooth, inclined. Teleoconch sculpted with a pronounced subsutural ridge and spiral grooves, which are very weak on the first teleoconch whorl, but become distinct after that. Spiral grooves number about 18 on the body whorl. The interspaces vary from 2 to 3 times the width of the grooves themselves and they are slightly wider on the upper half of the whorl. Whorls convex, but not strongly inflated. Aperture covered by thick callus, extending widely onto the base. Nodule on parietal lip large, angular, connected to a lamella extending into the aperture. Columellar lip bears two smooth folds, with the upper one less developed than the lower one. Outer lip thick, smooth, with a swelling present on the middle of the lip. Exterior of the outer lip bears weak striations. Aperture rather narrow, constricted by swollen outer lip, which projects beyond columella. Anterior and posterior sinus well-defined.

Differentiation. This species is rather similar to Ringicula yokoyamai (Takeyama, 1935) in its size, shape and apertural characters, but R. yokoyamai (Takeyama, 1935) has fewer spiral grooves and it lacks a subsutural ridge. All other species of Ringicula are easily set apart from R. opima nov. spec. by a lack of callus on the base and/or the absence of a subsutural ridge.