DIAGNOSIS. Shell: Of medium size, spire of medium height to relatively tall, whorls lightly convex, with indistinct sutures and bearing granular spiral cords. Body whorl bi-angled, upper (peripheral) angulation weak, with or without short, hollow spines, 20 small spines on the last whorl of one Japanese specimen, none on another Japanese specimen, and 12 in the only Australian specimen. Spines persistent at suture on early whorls. Spines are narrowly triangular, slightly downwardly directed. Basal angle sharp, with a prominent row of gemmae that are pointed (but not spinose) in the Australian specimen but rounded in Japanese material. Two rows of gemmae between peripheral and basal angles, a weak third in Australian shell; 9-10 closely-packed gemmate spirals on flat base and 7 on side of penultimate whorl, with interstitial spiral threads developing on body whorl of most specimens. Subsutural cord stronger than others on upper whorl surface, situated at base of very narrow, steep subsutural area. Surface of shell between gemmae sculptured with faint, prosocline axial growth lamellae. Basal callus rather thin, spread over about 1/5 of the base, separated from columella by a groove when immature, a continuous glaze when mature (not fully developed on large Japanese shells examined), bright orange (pale yellowish-white in the dead Australian shell), columella nacreous white. Outer lip very slightly reflected in mature Australian shell, simple in Japanese shells. Surface pinkish-fawn, with pale yellow-brown base; very faint purplish, radial blotches on upper surface. Operculum: White; almost circular, with a high but slightly concave edge, and convex upper surface; edge concentrically sculptured, upper surface irregularly pustulose.
DIMENSIONS. Holotype: height 33.0 mm, diameter 32.0mm; paratype: height 33.6 mm, diameter 37.5 mm; figured Japanese specimen: height 34.7 mm, diameter (excluding spines) 33.1 mm; Australian specimen: height 36.3 mm, diameter (excluding spines) 35.5 mm.
TYPE LOCALITY. Off Uotsuri Isle, Senkaku Ids, S.W. Japan, trawled.
TYPE. Holotype, Shikama Colin, Geological Institute, Yokohama National University, with one paratype.
OTHER MATERIAL EXAMINED. Off Torishima Is., Izu Ids, central Japan, 250 m (NSMT) (1); Japan (NSMT) (2); Tosa Bay, Shikoku, Japan (ANSP) (4); Arafura Sea, off Arnhem Land, Northern Territory, Australia, 8°14'S, 133°12'E, 125 m (AM, C.72710) (1); "Siboga" Stn 100, 6°11'N, 120°37.5'E, Indonesia, on dead coral, 450 m (Zoologisch Museum, Amsterdam), the specimen recorded as Astralium (Bolma) modesta var. girgyllus by Schepman (1908).
OTHER LOCALITIES. Stn D86 (L1), 33°22.0'N, 133°39.1' E, 150-190 m, Kurose Bank, off Hachijo Island, Japan (Okutani, 1975).
The Japanese shells loaned to us from the NSMT (fig. 13a-c) and shells figured by Oyama & Takemura (1960, Bolma, figs. 1,2), Habe (1961, pl. 7, fig. 18; 1964, pl. 7, fig. 18) and Shikama (1973, pl. l, fig. 3, 4) differ from the single specimen from the Arafura Sea only in having shorter and more numerous peripheral spines. As the peripheral spines of Bolma vary greatly between individuals we consider the Japanese and Australian specimens to be conspecific.
Bolma tamikoana differs from all other species of Bolma in its relatively weak sculpture, reduced spines, almost straight spire outlines, simple sutures, and almost absent peripheral angulation and prominent basal angle. From the South African B. tayloriana, with which it has been confused by several Japanese authors, it differs in its taller spire, coarser sculpture, different dorsal coloration, thicker shell, much smaller basal callus, in bearing a row of small peripheral spines, in having a basal angulation, in the different operculum, and in lacking an obvious periostracum.