Description. Claviform, adult length 9.4-20.4 mm, with orthoconoid spire (breadth/length 0.37-0.43, aperture/total length 0.35-0.46) and broadly tapering, truncate base, end of siphonal canal oblique, shallowly to deeply notched, fasciole evenly convex, occasionally with slight false umbilicus. Anal sinus linguiform, deep, adapically directed, weakly constricted by a parietal pad; outer lip distinctly alate, in side view gently convex, sometimes feebly crenulate, with deep stromboid notch.
Whorls concave subsuturally, tops of ribs sometimes bulging slightly below suture. Axial ribs suture-to-suture on early whorls, developing a shallow concavity at about 0.3 of each whorl below the suture, gradually weakening at suture, obsolete on rostrum or occasionally at level of parietal nodule, eight on first whorl, 10-13 on penultimate whorl, in t/s angularly rounded, wider than their intervals, becoming wavy or bifurcating on base; last whorl with a rounded varix, ca 0.25 back from lip. Base of last whorl with 12-14 weak spiral ridges, becoming even weaker adapically and evanescing towards shoulder, plus 5-7 rather weak, rounded ridges on rostrum; sometimes a few faint spiral striae below suture. Maximum length.
Colour variable: light to dark brown (usually concentrated in a band around middle of last whorl) with paler brown to white ribs, base of last whorl off-white to buff; often whitish overall, tinged between ribs with brown. Aperture brown, margin white.
Protoconch distinctly papilliform, with two smooth whorls, first one depressed, surface smooth, but under higher magnification, it is seen that sutural region is slightly pustulose and there are a series of very fine plicules below suture. Diameter ca 690 µm, height 730 µm. Protoconch-teleoconch transition is marked by strongly sinuous axial riblet.
Measurements. Largest and smallest undamaged adults: 17.3 x 6.0 mm and 9.4 x 4.0 mm, respectively.

Originally described without locality, Pleurotoma obliquicostata was recorded by Schepman (1913) from Sulu Is. (Philippines) and Kei Is. (Indonesia), also as "subfossil specimens" from Celebes [Sulawesi]. In the following year Melvill & Standen (1895) reported P. obliquicostata from Lifou. Although Bouge & Dautzenberg (1914: 140) rejected this record as "certainement errone", comparison between syntypes of Pleurotoma obliquicostata and author's specimens (syntypes?) of Clavus leforestieri, reveals no difference. Judging by the New Caledonian samples examined, Clavus obliquicostatus is the most abundant of the larger drilliids in the area.

Distribution. Eastern Indonesia and Philippines to New Caledonia, 2 to ca 100 m, sand, coral and corall debris, in our material confirmed live to ca 60 m.