Diagnosis. A Calliostoma species of large size, with a globose shape, a moderately elevated spire, 4 strong, smooth spiral cords, one of them making shoulder at first third, a convex base with very weak smooth spiral cords, a rather wide umbilicus; light hazel with a beige base.
Description. Shell of great size for the genus (height 30.7 mm, width 33.3 mm), wider than high, globose in shape; spire moderately elevated, height 0.9x width. 1.7x aperture height; rounded periphery; rather wide umbilicus.
Protoconch about 350 µm wide, of 1.5 whorls, rounded, eroded.
Teleoconch of up to 6 convex whorls. Suture visible, not canaliculated, first whorl convex, eroded, spiral cords poorly visible but indistinct at end of whorl. On second whorl, weak wide prosocline ribs and 4 subgranular spiral cords; P3 and P4 stronger than P1 and P2, P3 making weak shoulder; distance between cords similar in size to cords. On third whorl, P3 the strongest, making keel; P3 and P4 almost smooth; P3 making keel on shoulder; Si (i=l, 2, 3, 4) appearing, very thin, subgranular; P2 very weaker than other primaries; S4 poorly visible, almost completely hidden by succeeding whorl. On fourth whorl, axial ribs no more visible; P3 making stronger keel; P1 and P4 slightly weaker than P3, other cords much weaker; tertiary cords appearing everywhere on whorl. On fifth whorl,
S4 partly emerging from suture, stronger than P2 and other Si; secondary and tertiary cords of abapical half flat, rather wide; secondary and tertiary cords of adapical half rounded, thin, weak; distance between all cords smaller than cords. On last whorl, S4 fully visible; P3, P4 and S4 similar in strength, P1 slightly weaker; all other cords much weaker; rounded periphery.
Aperture subcircular; outer lip rather thin without any angle; inner lip thickened in its adapical part, making a basal flange. Columella almost vertical, slightly curved.
Base convex, with about 25 smooth spiral cords; outermost cord thick, smooth; other outer cords hard to distinguish, innermost cords more visible. Umbilicus rather wide (about 12% of total width), deep, funnel shaped umbilicus, partly covered by an expansion of the columella.
Colour of teleoconch whorls light hazel, base beige; protoconch white translucent.

Calliostoma polysarkon n. sp. is rather close to C. hajimeanum Yoshida, 1948 from Japan, but this similar in size species has only 2 (not 4) main spiral cords, P4 (not P3) making keel on the shoulder and S4 peripheral, and much more numerous spiral cords (at least 50) on the base.
The new species may be compared to Calliostoma nobile (Hirase, 1922) from Japan, but this species has a less elevated spire, weaker main spiral cords and no shoulder on whorls, a nearly smooth base except some cords around the umbilicus and a wider umbilicus, without columellar projection on it. Considering that C. polysarkon n. sp. looks a little like Falsimargarita stephaniae Rios & Simone, 2005 from Argentina (although this much smaller species is more depressed, has not the same main spiral cords on the whorls and less numerous, much stronger spiral cords on base), it could happen that the new species belong to the genus Falsimargarita Powell, 1951. Only soft part and radula studies of additional specimens might lead to use this genus for the new species.

Type locality. Vanuatu, South-East of Malekula