Shell sharply conical, very solid, opaque. Larval shell with 1.5-1.75 convex whorls. The initial part is covered by live line zigzag lines abruptly changing into live coarse lines, partly consisting of close-set zigzag lines, partly as very rough lines, on which next to nothing of zigzags can be traced. On the subsutural part towards the first subsutural spiral line, some irregular spread micro-papillae can be detected. Average diameter of the- protoconch 0.4 mm. Teleoconch consisting of 3-3.5 whorls of which the body whorl is clearly biconical. Axial sculpture of 14-16 prominent axial ribs, crossed by 8-9 thin spiral ribs, regularly spread over the entire body whorl. Micro-sculpture of 7-10 spiral threads covering the total height of the teleoconch, including the spiral ribs. Aperture ovate, with a thin parietal callus inner lip somewhat reflected over the narrow umbilical crevice. Peristome simple ant continuous; outer lip ending in a strong varix, overrun by the spiral ribs.
Dimensions. — H 1.50-1.85 mm, W 1.00-1.50 (N = 7): holotype: H 1.70 mm, W1.20 mm.
Differentiation. — Alvania denhartogi n. sp. resembles A. pagodula (B.D.D., 1884) but the latter has a protoconch with thin spiral threads, 6-7 spiral ribs, 12-14 axial ribs a less strong varix and lacks the micro-sculptural lines on the teleoconch.
Etymology. The species is named after Mr.J.C. den Hartog, for his participation in the CANCAP expeditions.