Medium-sized, depressed cone-shaped shell with widely open umbilicus; whorls somewhat inflated, with spiral sculpture dominant; subsutural rib ± distinctly separated, midrib-area divided by 1-3 spiral grooves; upper point of whorl attachment on central to lower part of lower peripheral rib; proxumbical rib absent. Color pattern of distinct brown blotches on upper and lower peripheral ribs (in darker-colored specimens also in area next to umbilical crenae). Protoconch diameter 1.18-1.36 mm; yellowish to brown.

Teleoconch: medium-sized, diameter of specimens in collections usually 11-16 (rarely up to 20) at 3 3/4 to 4 3/4 (5) whorls. Shape: depressed cone-shaped, with whorls somewhat inflated; umbilicus wide (UD ca. 27% of SD); Sculpture: Upper side: spiral sculpture dominant; SSR ± distinctly separated; MR-area distinctly divided by 1-3 spiral grooves, crossed by ± faint oblique axial grooves; Periphery: UPR not as strong and prominent as LPR; upper point of whorl attachment on central to lower part of LPR (upper part of LPR thereby forming part of upper-side sculpture); no distinct suture; Base: IPR ± strongly developed, often with an additional spiral rib between LPR and IPR; BF without spiral ribs; PUR absent; UC distinctly separated; columellar wall forming almost straight inner lip with plications for support of the columellar muscle, with deepest groove in UC overhanging umbilicus; no spiral sculpture on umbilical side of wall. Coloration: MR-area light-brown; SSR, PR and base lighter in color; SSR with faint, PR with distinct pattern of brown blotches (about 18-24 on 4th Tw; in darker-colored specimens also brown blotches on IPR and in area in front of UC). - Protoconch: medium-sized to large (1.18-1.36, x = 1.28); distinctly heterostrophic; anal keel well-developed; yellowish to brown. - Operculum: as described for genus. - Radula and Anatomy: not known.

The three Indo-Pacific forms Adelphotectonica nomotoi, A. reevei, and A. kuroharai are very similar to each other, but all specimens studied to date could be assigned to one of the three. They cannot be interpreted as ecological or geographical forms, because all of them were present in a single sample (New Caledonia; MNHNP unnumbered). The sublittoral morph of A. reevei reaches the greatest shell height; A. kuroharai attains the greatest shell diameter. A comparison of teleoconch diameter versus number of whorls revealed no significant statistical difference; all forms showed almost the same range of variation (ca. 10.0-13.5 mm). Differences are found mainly in upperside teleoconch sculpture, coloration and protoconch size. The three forms are here provisionally accepted as species; further material, and a study of anatomy and radulae, are necessary.

Geographical distribution: Known from disjunct localities in southern Africa, New Caledonia, New Zealand and the Midway Islands.
Habitat: Sublittoral to upper bathyal (depth records between 74 and 430 m), live records from 100-115 m.