DIAGNOSIS. Shell: height about equal to diameter, base almost flat, whorls strongly angled but concave between angulations. Peripheral angulation margining base, bearing 12 large, rounded, hollow, scale-like spines per whorl; upper angulation at half whorl height, bearing 9 to 14 large nodules, expanded laterally into prominent spines on juvenile shell but reduced to rounded, scale-tipped nodules on last few whorls of sub-adult specimen. A weak basal angulation represented by weakly gemmate spiral cord near margin of base of juvenile shell, and by weakly defined cord and marked colour change in sub-adult. Upper surface of whorls sculptured with low, narrow-crested axial folds extending from upper suture to each nodule of upper angulation, and entire surface densely covered with fine, wavy spiral lirae, more prominent on nodules than elsewhere; one cord between upper and peripheral angulations slightly more prominent than other spiral lirae. Base bearing narrow, smooth callus in central fifth of radius, remainder sculptured with about 10 low, narrow, finely scaled spiral cords and many fine interstitial lirae. Nodule rows and lower half of whorls bright purplish pink, shading to a more yellow tinge on upper half of whorls and to pinkish yellow on base; basal callus pale yellow.
Operculum: Not seen.
DIMENSIONS. Holotype: height 27 mm, diameter 31 mm (Smith, 1902); figured subadult: height 31.6 mm, diameter 34.3 mm; figured juvenile: height 12.1 mm, diameter 14.0 mm. Maximum size recorded 85 mm in height (Barnard, 1963, p. 220).
TYPE LOCALITY. Off Durban, South Africa, ex stomach of fish.
HOLOTYPE. Smith (1902, p. 249) stated that the holotype was in the collection of "Mr. Anderson, junr., of Durban." Its present location is unknown.
MATERIAL EXAMINED. Off Natal (NM, 3729) (figured sub-adult); off Durban, ex gut loggerhead turtle, 1973 (NM, A235) (2 juveniles).
OTHER LOCALITIES. South Africa; 32°45'S, 28°26'E, near Cape Morgan, 66 m; off Port Shepstone, 44 m; off Itongazi River, 46 m (all from Barnard 1963, p. 220).
Bolma andersoni is similar in shape, type of sculpture, and coloration to 6. jacquelineae (Marche-Marchad), B. modesta (Reeve) and B. girgylla (Reeve), but differs from all related species in its flatter and more finely sculptured base, in its single row of relatively large, rounded nodules above the peripheral row, and in its very reduced basal angulation. The larger of the two juvenile specimens available bears long spines on the nodules of the upper angulation , but these have been broken off the sub-adult specimen examined. Barnard (1963, p. 220) assigned shells up to 85 mm high to B. andersoni. The unidentified juvenile specimen figured by Barnard (1963, fig. 7 f, g,) is similar to available juveniles of 6. andersoni, and probably belongs in this species; it is from off Unkomaas, Natal, in 73 m (SAM, A9236).