Moderately small to large (50-150 mm), moderately light to heavy. Forms equestris (45-60 mm) and vidua (45-80 mm) smaller than other forms; form nigrescens (25-65 mm) moderately small to medium-sized and moderately light to moderately solid. Last whorl conical to ventricosely conical; outline nearly straight, variably convex adapically. Shoulder angulate, moderately to strongly tuberculate. Spire of low to moderate height, consistently low in forms vidua, nigrescens and equestris; outline straight to moderately concave. Larval shell of about 2.25 whorls. Postnuclear spire whorls tuberculate. Teleoconch sutural ramps concave in late whorls, with 2-4 weak spiral grooves and additional spiral striae; spiral sculpture often obsolete. Last whorl with weak spiral grooves on basal third to three-fourths. Ground colour white to pale violet or pale pink. Last whorl with a blackish brown network of lines, triangular areas and rhomboid blotches clustered in a spiral band on either side of central area; bands often with an orange to brown background. Base may be tinged with bluish grey. Apex white to light purple; larval whorls light yellow in Hawaiian shells (Perron, 1981 a). Postnuclear sutural ramps with a blackish brown network of lines and streaks. Aperture white, occasionally tinged with violet, pink or yellow; base of aperture may be brown. Periostracum yellow to orange, thin, translucent, smooth.
In form equestris colour bands with larger blackish brown blotches, interspersed with white tents of various sizes.
In form vidua last whorl with a broad blackish brown or occasionally bright orange spiral band above centre and another at basal third, both interspersed with small while to brownish while tents. Lower band often extends to base. White zones below shoulder and below centre with a variably incomplete network of fine zigzag lines and small spots; pattern ranging from obsolete wavy lines to continuous lines edging coalescent tents. Base tinged with bluish grey. Anterior end of aperture violet-brown or orange-brown; rest of aperture white, suffused with blue or orange. In form nigrescens colour pattern ranging from typically patterned to almost solid black shells. Aperture white to bluish white.
Dorsum of foot white to cream, heavily mottled with brown, lighter in transition zone from anterior to central part; marginal zone with a relatively broad black band ending in latero-anterior blotch; a black central spot at anterior end and a white fleck beneath the operculum. Sole of foot cream, transversely and longitudinally mottled with brown. Rostrum cream, mottled with brown on dorsal side. Tentacles white to brown, with a dark tip, dorsally mottled with brown. Siphon white, with or without a yellow edge and with a red, brown or black anterior ring as well as a posterior band or half-ring shading from tan to blackish brown. In form vidua, radular teeth with an adapical barb opposite a blade; serration about twice as long as blade, ending in a prominent cusp; base with a spur (Nybakken, 1990).

C. bandanus is a close relative of C. marmoreus, and some authors have included it in the latter species. The conchological differences are comparatively slight, consisting of more pronounced spire tubercles and a less regular pattern with 2 distinct dark colour bands in C. bandanus, while the pattern of C. marmoreus is generally uniform and lacks bands. Ecological differences also favour separation at the species level: C. bandanus usually lives in deeper waler and often occupies a different microhabital where both occur in sympatry. In Kwajalein, Marshall Is., C. marmoreus is found on inter-island coral reef and at the east side of the lagoon on sand bottom, while C. bandanus is restricted to rock and rubble bottoms of the ocean-side and the lagoon-side of the west reef; co-occurrence has not been observed (Johnson, 1977; J. & S. Johnson, pers. comm.; Pearson, pers. comm., 1991). In New Caledonia, the bathymetric ranges differ (1 -5 m in C. marmoreus, 5-18 m in C. bandanus). For comparison with C. nocturnus, see the latter species.
Specimens agreeing with the description of C. vidua cannot be clearly separated from C. bandanus by conchological characters. In the western part of the central Philippines, they intergrade with C. bandanus. Their co-occurrence, with intermediate shells, favours the ranking of C. vidua as a form of C. bandanus.
Specimens agreeing with the description of C. nigrescens show a gradual transition from the typical C. bandanus pattern to almost black shells. In Western Samoa, 6% of the population have nearly black shells, while in American Samoa, the pattern is like that of C. bandanus elsewhere. Shell size is similar in American Samoa and Western Samoa. The habitat is very similar in American Samoa and Hawaii (Purtymun, 1977). We provisionally consider C. nigrescens a form, occurring in Samoa, Solomon Is. and Admiralty Is.

Type Localities: C. bandanus: "Lisle de Banda, Tune des Moluques"; C. vidua: "Island of Capul, Philippines"; C. v. mozoii: "in Honda Bay, Arricife Island, Palawan."
Range: Natal to Somalia and to Hawaii and Tuamotu Archipelago, absent from Red Sea, India and Sri Lanka; form vidua in southern and central Philippines; form equestris in Moluccas; form nigrescens in Samoa, Admiralty Is. and Solomon Is.
Habitat and Habits: Shallow subtidal to 90 m (Hawaii: Kohn & Weaver, 1962), mostly encountered in 5-20 m. On coral reef and in reef lagoons, in sand, on weedy sand, rocks, and rubble. Animals active at night (New Caledonia; Tirard, pers. comm., 1989).