Large cone-shaped shell with widely open umbilicus; whorls on upper side gemmate, somewhat inflated; two spiral grooves below suture (midrib-area divided subequally, with upper midrib much narrower), and shallow depression at base of the lower midrib. Subsutural rib white, after about 5 whorls with pattern of roundish blotches; upper midrib nearly solid dark-brown; proxumbical rib and umbilical crenae pure white. Protoconch diameter 1.14-1.40 mm.
Teleoconch: Large, diameter of specimens in collections usually 25-40 at 5 1/2 to 7 3/8 whorls. Shape: moderately depressed to fairly high-spired cone-shaped, with whorls somewhat inflated (especially on upper .side); umbilicus wide (UD ca. 29% of SD). Sculpture: Upper side: SSR distinctly separated; LMR wider than UMR (ca. 3:1); shallow depression at base of LMR; Periphery: PR strong, with UPR almost as prominent as LPR; one additional fine spiral rib between UPR and LPR; upper point of whorl attachment on upper part of LPR (upper edge of LPR visible in suture of early whorls); upper side and periphery crossed by deeply incised oblique axial grooves, resulting in formation of many elongate oblique segments, becoming smooth on body whorl of larger specimens; Base: IPR strong, with one additional spiral rib between LPR and IPR; BF without spiral ribs (smaller specimens with radiating plications, stronger towards umbilicus); two distinctly separated nodulose spiral ribs (PUR and UC) surrounding umbilicus, with UC relatively fine and regular; 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: SSR initially white, with pattern of ± round brown blotches (ca. 10-14 per whorl, each 1-2 nodules wide), starting after about 5 Tw; UMR initially variegated with shades of brown, later ± solid dark-brown; LMR olive-brown; UPR blotched with light- and dark-brown (always lighter in color than SSR); LPR and IPR almost white, with weak narrow brown blotches; BF flamed with bluish-white; one dotted spiral line in front of PUR; PUR and UC pure white. -Protoconch: medium-sized to large (1.14-1.40, x = 1.26); distinctly heterostrophic; with rounded ridge in anal-keel area; whitish, with brown outer corner in front of varix. - Operculum: as described for genus. - Radula & Anatomy: not known.

The shell sculpture of Architectonica modesta is similar to those of A. picta and A. taylori, but the axial sculpture is weaker. This species is easily recognized by the combination of a white subsutural rib (that often has a few regularly spaced brown blotches) and a more or less solid-brown colored upper midrib. It is frequently confused with A. perspectiva, which has no spiral groove in the midrib-area below the brown band and which has dark-brown umbilical crenae, while those of A. picta are pure white.

Geographical distribution: Subtropical and tropical Indian Ocean and West to Central Pacific.
Habitat: Upper sublittoral (most depth records between 1 and 85 m), live records from sandy substrates in shallow water.