Shell up to 12.7 mm high, glossy, stout, spire rather broadly conical, 1.43-2.05x as high as aperture, mean spire angle 59-71°, narrowly umbilicate.
Colour of protoconch and 1st teleoconch whorl pale buff white or white; subsequent whorls pale buff white or white, irregular yellowish, brown patches on shoulder and on outer part of base extending from below P3; smaller, mostly paler spots elsewhere on spire and base; last part of last adult whorl occasionally locally flushed pale pink. Protoconch 370-400 µm wide, sculptured with network of fine, crisp threads that enclose roughly hexagonal spaces.
Teleoconch of up to 7.70 whorl; 1st eighth whorl with crisp spiral threads, delineated by strong, rounded varix and growth scar. First 2 whorls convex, subsequent whorls strongly angulated at P2, P3 peripheral, periphery evenly rounded at maturity, base convex, umbilical rim angulate. Spire and base with prominent spiral cords that multiply by intercalation; axial costae strong on 1st 4 or 5 whorls, considerably weaker or almost obsolete thereafter. P2-P4 commencing immediately after post larval scar, strong throughout; P1 a fine thread on 1st 2 whorls then gradually enlarging though remaining weaker than P2-P4; P4 partly covered by succeeding whorls. Secondary spirals remaining weaker than primaries. S1 commencing mid 4th - mid 5th whorl, S2 commencing mid 3rd - mid 5th whorl; S3 absent, positionally represented by fine tertiary spiral on last adult whorl. Tertiary spirals commencing after 5th whorl at varying stages and positions, enlarging to resemble secondaries, 1 per interspace. Nodules on spire roundly conical, axially compressed; strong and uneven-sized on P2 and P3 after 2nd whorl, those on P2 upturned and approximately each 3rd - 4th nodule extremely large; PI more weakly nodular, secondary and tertiary yet more weakly nodular. Base with 10 or 11 similar rounded spiral cords with low, rounded nodules. Fine collabral growth lines throughout. Umbilicus deep, wall almost vertical, smooth apart from obscure spiral lines, diameter 14.0-25.2 % of shell diameter. Aperture subcircular. Outer lip thin at rim, thickened within. Inner lip thick. Parietal inductura extremely thin. Animal creamy white. Snout dorsoventrally flattened, slender, about twice as long as broad, tip laterally expanded and set with large slender papillae. Cephalic tentacles similar, slender, narrowly tape¬red, large eyes in prominent outer basal eyestalks. No right neck lobe. Left neck lobe large, about as long as cephalic tentacle, folded, thin in section, Epipodial tentacles slender, enlarging anteriorly, 4 on each side. Foot large, long and narrow, tip blunt, prominently anterolaterally eared, sides irregularly pustulate. Operculum typical, reddish brown,
Radula with the formula oo + 5 + 1 + 5 + oo. Central and lateral teeth thin in section, flexible, tips finely serrate. Tip of central tooth narrowly angulate, tips of lateral teeth extremely slender. Innermost pair of marginal teeth stout, with 5 or 6 stout cusps. Next marginal narrower and longer, tip smaller and with 5 or 6 stout cusps. Outer marginals slender, tips with small slender cusps. Jaw plates with elongate elements at leading edges.

This species is similar to C. (B.) katherina from off New South Wales and Queensland, and is obviously closely related. C. (B.) diadematum differs from the Australian species, however, in numerous points of detail, including more exsert protoconch, coarser sculpture, considerably wider umbilicus, with the shoulder (P2) at adapical 3rd instead of submedian on later whorls. The two subadult specimens from off Chesterfield Islands and southern New Caledonia (Figs 44-45) differ from the Argo and Capel Banks type material in having less prominent nodules on P2, and in having S2 stronger at the same stage of growth. These specimens could equally well represent divergent isolated populations of C. (B.) diadematum or distinct species.

Capel Bank (type loc), Argo Bank, Chesterfield Islands, and off southern New Caledonia, 120-580 m, living at 258-320 m.