Diagnosis: Shell moderately large (55 mm), b/1 0,27-0,33. a/1 0,27-0,36, whorls with a rounded shoulder, siphonal canal moderately long, tip very obliquely truncate, with very shallow notch; aperture narrow, fasciole sometimes fairly strong, labrum weakly erenulate at most, stromboid notch very slight, anal sinus roundly U-shaped with greatly constricted opening, parietal nodule very large, angular, projecting outwards, situated at suture; subsutural cord massive, equal in width to deep, concave shoulder sulcus; axial ribs strong, moderately opisthocline, terminating at sulcus, 12-15 on penultimate whorl, bearing strong transverse nodules where crossed by spiral cords, which in rib intervals are somewhat tabulate and equal to their interstices in width, 4-6 spirals below shoulder on penultimate whorl, 3-5 fine threads in sulcus; intermediary spirals few or absent, with no microspirals, growth-threads inconspicuous; terminal varix about one-quarter whorl back from lip, an occasional varix on spire. Brownish-buff with subsutural region and a median zone cream, varices followed by an axial brown blotch. Protoconch evidently conical of at least 3 whorls, breadth about 1,1 mm.
Description: Shell narrowly claviform. b/1 0,27-0,33, a/1 0,27-0,36, with a narrow aperture and moderately long, fairly broad rostrum, bent slightly to right and terminating very obliquely; nearly 11 teleoconch whorls; suture moderately deep; whorls convex, roundly shouldered with median periphery, a deep, narrow, concave shoulder sulcus and strong, angular subsutural cord (which in apical view is slightly undulating), cord and sulcus more or less equal in width; left side of base of body whorl concave, fasciole sometimes fairly strong, false umbilicus shallow but distinct. Aperture narrowly pyriform, greatest width at about posterior third, lips equally concave, columella almost straight, siphonal canal moderately wide, expanding terminally and opening slightly to right, very shallowly indented; labial callus thick, its outer edge free, with a large, pointed, outwardly projecting parietal tubercle, situated at suture and intruding into opening of anal sinus which it constricts; edge of labrum gently convex in side-view, not or only feebly crcnulated. with a slight, very shallow indication of a stromboid notch, anal sinus deep, shaped like the Greek letter Omega, bordered below by a slightly alate angle.
Sculptured by strong axial ribs, ending abruptly at shoulder, crossed by weaker spiral cords, which form conspicuous transverse nodules where they cross; body whorl with a strong, rounded varix about one-quarter whorl back from lip, spire also with an occasional varix; no spiral microsculpture. growth-lines coarse and regular but inconspicuous, forming fine plicules below suture. Axial ribs more or less equal to their intervals, with strongly rounded to somewhat angular crests and sloping sides (the leading face somewhat steeper than the trailing one), moderately opisthocline. straight on spire, gently sinuous on last whorl, extending well onto rostrum; 8-9 ribs on 1st whorl. 12-15 on penultimate one, becoming weak and irregular after subterminal varix. Spiral cords relatively low and somewhat tabulate where they cross the rib intervals, subequal in strength to one another and to their interstices, except in shoulder sulcus, which bears 3-5 fine, close threads, and on crests of ribs where cords expand slightly to form rounded nodules; intervals between spirals with only an occasional intermediary thread, these being sometimes totally lacking; spiral lirae 3 on 3rd whorl (? absent on earlier whorls), 4-6 below shoulder on penultimate whorl, 15-19 on base of body whorl, those on rostrum relatively close and slightly weaker than elsewhere.
Colour moderate to light yellowish-brown, nodules, subsutural region and a zone at level of parietal nodule paler; each varix usually followed by an axial blotch of moderate yellowish-brown. Protoconch worn in all types, but apparently conical, of about 3 convex whorls, of which the last is relatively large, giving protoconch a slightly pupiform appearance; last half-whorl evidently with fine axial riblets; breadth approximately 1,1 mm, height about 1.0-1,2 mm.
Dimensions: 43,7x13,1 mm (holotype); 55,8 x 14,9 mm, 42.5x11.8 mm (largest and smallest adult paratypes respectively).
Operculum oblanceolate, anterior end acute with terminal nucleus, colour strong to deep yellowish-brown. Radula of about 46 rows of marginal plates; distal end of shaft rather tapering, cutting edge not sharply differentiated, accessory limb slender and very long.

Comparison of local material with the lectotype of Inquisitor aesopus (Schepman, 1913), and with a Philippine example of that (NM K1530), reveals a number of significant differences. From both I. aesopus and I. arctatus, I. nodicostatus differs in its broader shell, stronger subsutural cord (weak in aesopus). stronger, rounder and less sloping axial ribs, much stronger, more uniform spiral lirae, forming conspicuous nodules (smaller in arctatus, absent in aesopus). Furthermore, in nodicostatus the intervals between spirals contain few if any intermediary spirals (in aesopus 1-2 threads per interval), the parietal tubercle is much longer and more pointed, often projecting beyond outer lip, and the protoconch is more conical, with rounder whorls.

South-Africa. Outer continental shelf and slope of Natal, 195-310 m.