Shell medium-sized for genus, sturdy, white; protoconch diameter 0.4 mm, teleoconch whorls 7,5. Early whorls flat-sided except for strongly projecting subsutural cord; final whorl rounded, losing sharp basal angularity of previous whorl. First 3 teleoconch whorls with 3 strong, unbeaded spiral cords, intercalary cords of lesser strength appearing on fourth whorl; original cords becoming beaded on fourth whorl; penultimate whorl with 9 somewhat irregular cords, uppermost of these beaded; body whorl with about 13 cords above ill-defined periphery, uppermost of these finely beaded. Base imperforate, mostly smooth but for fine spiral striae, basal cords more strongly developed toward columella. Aperture rounded, outer lip thin, columella thick. Interior iridescent pink and green. Dimensions: Height 25.7 mm, diameter 22.8 mm (holo-type); height 26.5 mm, diameter 22.8 mm (paratype).

Calliostoma bernardi is closest to C. titanium McLean, but is smaller and has pronounced spiral sculpture at all growth stages, rather than having the nearly smooth third and fourth whorls of both C. titanium and C. platinum Dall, 1890.

Calliostoma titanium: Shell large for genus, sturdy, white, protoconch diameter (of smallest specimen) 0.4 mm, teleoconch whorls 7. Whorls only slightly rounded, shoulder slightly tabulate; base defined by moderately sharp keel. First 3 teleoconch whorls with strong, unbeaded spiral cords; spiral sculpture of subsequent whorls very subdued except for subsutural cord; subsutural cord prominently beaded on fifth whorl; fine, even spiral cords emerge on fifth whorl; 16 spiral cords on penultimate whorl; all cords microscopically beaded on final whorl. Suture laid upon basal angulation; base imperforate, smooth, with fine spiral striae, more strongly developed near columella. Aperture quadrate, outer lip thin, columella thick, slightly reflected. Interior iridescent pink and green. Dimensions: Height 32.2 mm, diameter 30.0 mm (holotype); height 27.4 mm, diameter 25.3 mm (paratype).

Calliostoma platinum: Shell large, thin, polished, iridescent white, with seven whorls beside the nucleus; nucleus minute, lost; subsequent whorls slightly flattened behind the periphery, full and rounded on the base; longitudinal sculpture of obscure spiral lines behind the periphery and somewhat stronger flattish threads, separated by shallow grooves, on the base; at the periphery is a single prominent thread, immediately in front of which is the suture, the succeeding whorl being appressed against the thread ; the single specimen obtained has a second prominent thread about two millimeters behind the peripheral one on the last whorl, but it is probable that the development of this thread was stimulated by an injury of which traces are plainly visible just before the second thread begins; base full and rounded; aperture rounded quadrate; the outer lip thin and sharp, its plane oblique and slightly flexuous; body with a very faint wash of callus; pillar slender, pearly, slightly arched, very little reflected, simple; interior polished, iridescent, without lirse; the external sculpture faintly perceptible owing to the tennity of the shell. Maximum longitude of shell, 32; maximum latitude, 29mm.

Calliostoma platinum: Material Examined. Although not recorded from the Santa Maria Basin, the area is within the distribution of this offshore species. There are 18 lots in the LACM collection from throughout the distribution.
Description. Relatively large, thin shelled; early whorls with 2 carinations that become obsolete on later whorls; periphery defined by single projecting thread upon which succeeding suture is laid. Spiral sculpture consisting of fine striae, most strongly developed on base. Height 25-32 mm.
Type Locality and Type Specimens. "Near Santa Barbara Islands, California," 414 fathoms. Holotype: USNM 96558.
Distribution. Moresby Island, Queen Charlotte Islands, British Columbia (53°N), to San Diego, California (33°N).
Habitat Soft bottoms, 180-700 m. Feeding biology is unknown, but would be of unusual interest, as this species is unlike most members of the genus in its soft rather than hard bottom habitat.
Remarks. A related species is Calliostoma titanium McLean, 1984, which has a sturdier shell and finely beaded spiral cords; it is known only from the original material from the vicinity of Santa Catalina Island and Cortez Bank. Calliostoma chilena Rehder, 1971, from Chile, is very similar to C. platinum.

Calliostoma titanium: Shell large for genus, sturdy, white, protoconch diameter (of smallest specimen) 0.4 mm, teleoconch whorls 7. Whorls only slightly rounded, shoulder slightly tabulate; base defined by moderately sharp keel. First 3 teleoconch whorls with strong, unbeaded spiral cords; spiral sculpture of subsequent whorls very subdued except for subsutural cord; subsutural cord prominently beaded on fifth whorl; fine, even spiral cords emerge on fifth whorl; 16 spiral cords on penultimate whorl; all cords microscopically beaded on final whorl. Suture laid upon basal angulation; base imperforate, smooth, with fine spiral striae, more strongly developed near columella. Aperture quadrate, outer lip thin, columella thick, slightly reflected. Interior iridescent pink and green. Dimensions: Height 32.2 mm, diameter 30.0 mm (holotype); height 27.4 mm, diameter 25.3 mm (paratype).

Shell thin, height 25-37 mm. Ground color white (periostracum removed); whorls convex; teleoconch 2-3 unbeaded threads; whorls, subsutural threads 0-5 weak/absent, threads smooth rarely lightly beaded; peripheral cords 1-3 smooth; threads immediate above/below, absent/microscopic; base angular, basal threads 35+ absent/minute; columella scar pearl-sliver; notable carina present/absent adjacent to columella.
Distribution. From Icy Bay, Gulf of Alaska (59°17.61'N, 141°56.04'W: Clark 2018), south to San Diego (33°N), California. 180-700 m. Akoya platinum undoubtedly occurs south of San Diego, California, at appropriate depth along the northern Baja California peninsula. Scarce.
Remarks. The shells illustrated represent the ideal phenotypes for A. platinum, form titanium and form bernardi. Variation in color (gray/gray-brown vs white results from the presence or absence of the
periostracum. Tuskes & Tuskes (2019) illustrated the intermediate forms and provide additional quantitative results. Forms titanium and bernardi have progressively increasing number of cords/threads and beading.

Calliostoma titanium: Although Calliostoma titanium has its third and fourth whorls without spiral sculpture, as in C. platinum Dall, 1890, it differs from the latter in having a sturdier shell, a subsutural tabulation, and numerous fine cords on the final whorl. It is larger than C. bernardi McLean, from which it also differs in having the third and fourth whorls smooth rather than having strong spiral cords on all whorls; the cords on the body whorl are more numerous and finer than those of C. bernardi.

Calliostoma platinum: The operculum of this species has about fourteen very narrow whorls, is polished internally and somewhat rough externally from the projecting margin of the coils. It bears about the same proportion to the aperture as in the shallow water species. The shell itself is less attractive than most of the group, but indicates that some individuals of the species may have a delicate pale iridescence. The exterior of this specimen, shows little pearliness and is chiefly of a somewhat livid white, like the eye of a boiled fish.

Calliostoma titanium: Although Calliostoma titanium has its third and fourth whorls without spiral sculpture, as in C. platinum Dall, 1890, it differs from the latter in having a sturdier shell, a subsutural tabulation, and numerous fine cords on the final whorl. It is larger than C. bernardi McLean, spec. nov., from which it also differs in having the third and fourth whorls smooth rather than having strong spiral cords on all whorls; the cords on the body whorl are more numerous and finer than those of C. bernardi.

Although only two specimens from well separated localities are known, the fact that they are conspecific argues against the possibility that this is a variant of C. titanium, which would be a major concern if only the southern specimen were known. I prefer not to designate paratypes from other than the type locality, but make an exception in this case.

Calliostoma titanium: Type locality: 256-274 m (140-150 fm) on green mud, 8.3 km (5 miles) SE of Santa Catalina Island, California

Calliostoma platinum: USA, near the Santa Barbara Islands, California.

Calliostoma titanium: Type locality: 256-274 m (140-150 fm) on green mud, 8.3 km (5 miles) SE of Santa Catalina Island, California (33°15'N; 118°14'W).

Type locality: 241-271 m (132-148 fm), off SE end of Santa Catalina Island, California