Shell (immature holotype) 8.00 mm high, glossy, stout; spire narrowly and evenly conical, 2.48x higher than aperture, mean spire angle 54°, anomphalous.
Colour of protoconch and 1st teleoconch whorl pale buff, 2nd and most of 3rd whorl white, subsequent whorls pale buff; S3 and P4 yellowish brown between nodules, base white.
Protoconch 420 µm wide, sculptured with network of fine threads that enclose roughly hexagonal spaces, apical fold tip tightly rounded, terminal varix strong.
Teleoconch of 6.50 whorls; 1st quarter whorl with crisp spiral threads and strong varix, delineated by growth sear and low varix, First whorl strongly convex. 2nd whorl becoming weakly convex, subsequent whorls flat with flush suture; periphery ungulate. S3 and P4 peripheral, base weakly convex. Spire and base with prominent, rounded, nodular spiral cords that multiply by intercalation; axial costae strong on 1st 3.5 whorls, weakening and becoming obsolete over next whorl. Nodules on spire rounded on 1st 3 whorls; thereafter in lateral profile sharply shelved adapically, rounded abapically, on S3 and P4 elliptical and axially compressed in plan view and semicontiguous, elsewhere rounded. Basal nodules considerably smaller, rounded. P2-P4 commencing immediately after post larval growth scar; P2 and P3 strong and similar throughout; P4 narrower, almost entirely exposed on spire; P1 commencing at start of 2nd whorl, as large as P2 and P3 by 3rd whorl. Secondary spirals enlarging to resemble primaries, S1 commencing early 6th whorl, S2 and S3 commencing mid 3rd whorl. Fine collabral growth lines throughout. Base with 16 spiral cords in front of parietal area, outer 3 weaker, closest. Aperture subquadrate. Outer lip thin at rim. thickened within. Inner lip thick. Parietal glaze very thin,
Animal (holotype). Snout dorsoventrally flattened, nearly twice as long as broad, tip laterally expanded and edged with crowded, slender papillae. Cephalic tentacles narrowly tapered, rather short, little longer than snout; eyestalks at outer bases continuous with prominent cephalic lappets. Left and right neck lobes very large, thin in section. Epipodial tentacles small, 3 right and 4 left. Foot large, long and narrow, sides with rounded pustules. Operculum typical, reddish brown.
Radula similar to that of C. granulatum but with 6 instead of 5 pairs of lateral teeth, each with more narrowly tapered cutting area.
Height 8 to 20 mm.

Distribution. South-eastern New Caledonia, 400-618 m (dd) (range computed using also data of B.A. Marshall, 1995); eastern New Caledonia, 100-180 m (dd); west of New Caledonia, 372-404 (dd); northern New Caledonia, 350-380 m, lv at 380-430 m (using also data of Vilvens, 2009b); off Lifou, Loyalty Islands, 425 m (lv) (Marshall, 1995); off Raoul Island, Kermadec Islands, 390-490 m (dd) (Marshall, 1995); Fiji, 168-353 m (dd) (Vilvens, 2005); Tonga, 500 m (dd) (Vilvens, 2005).

Diagnosis. The main characteristics of this species are a height up to 19.6 mm, a width up to 15.2 mm, an elevated, slightly coeloconoidal shape, an angulate periphery, a teleoconch of up to 9.4 whorls (first whorls convex and next whorls flat to slightly concave), 7 granular spiral cords on the last whorls (P2, P3, P4; PI; S3, S2; SI), S3 and P4 a bit stronger and very close, spiral interspaces narrower than spiral cords, a subquadrate aperture, an oblique columella without tooth, a weakly convex base with 16 granular spiral cords (innermost cords stronger), anomphalous, a yellowish white colour with S3 and P4 yellowish brown between beads.

Remarks. This species was described from an immature specimen (6.5 whorls) collected in southern New Caledonia: the shape is conical and the whorls are more or less flat. The biggest specimen (19.6 x 15.2 mm) mentioned by Marshall (unfortunately not illustrated in his paper) seems to be exceptionally large and apparently specific to the Kermadec Islands. The present new record from South Lansdowne (EBISCO: stn DW2631) is not so large (height 11.0 mm for 7.4 whorls) but has much more concave last whorls while matching perfectly the ontogeny of the spiral cords.

Although similar to the holotype in gross facies and apparently conspecific, the specimens from Lifou and Raoul Island exhibit some sculptural differences. In the Lifou specimen, PI enlarges more rapidly on the 1st whorl, and S2 and S3 commence earlier (early 3rd and mid 2nd whorls respectively), but the first four whorls are otherwise similar. Following the 4th whorl, P1, P2, S2 and P3 become much wider, gradually dividing medially, while they are sharply shelved both adapically and abapically (shelved adapically, rounded abapically in holotype). Since multiplication of spire spirals by fission is extremely rare in normal calliostomatids, it seems probable that the Lifou specimen has grown abnormally, perhaps due to injury associated with a repaired fracture early on the 3rd whorl. The Raoul Island specimen , similar to the holotype in early teleoconch facies, differs from it in the later appearance of S2 (early 8th whorl) and tertiary spirals (late 7th whorl), and differs from both the holotype and the Lifou specimen in having considerably stronger, more widely spaced nodules on S3 and P4. The Raoul Island specimen is interpreted as either an inter or intrapopulational variant.
C. xanthos corresponds in a general way with the original description and illustration of C. quadricolor Schepman, 1908. Unfortunately the only known syntype (ZMA, "Siboga", stn 49A, Sape Strait, Flores, Indonesia. 69 m) is clearly neither the originally described nor the illustrated specimen, which was thus presumably the one recorded from "Siboga", stn 257 (off Kai Is, Indonesia, 52 m) and evidently lost (MOOLENBEEK pers. comm.). The extant syntype (height 6.60 mm, diameter 6.10 mm), now bleached and etched due to prolonged storage in acidic alcohol, differs from C. (A.) xanthos in the earlier appearance of PI, and in that S3 becomes peripheral and larger than P4.
The Raoul Island specimen was originally thought to be related to C. simplex Schepman, 1908 (MARSHALL, 1979), but the holotype of that species differs in colour and sculptural details. C. simplex is much closer to C. (F.) comptum and thus probably belongs in subgenus Fautor.

Off Lifou. Loyalty Islands (425 m), south of Ile des Pins, southern New Caledonia (470 m, alive), off Raoul Island. Kermadec Islands (390-490 m).