Very large to extremely large, moderately depressed 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 narrower), and wide groove at base of lower midrib. Subsutural rib whitish with brown pattern, midribs tan without color pattern, proxumbical rib variegated light- and dark-brown; and umbilical crenae whitish-brown with darker markings. Protoconch diameter > 1.20 mm.

Teleoconch: Very large to extremely large, diameter of specimens in collections usually 50-65 (rarely up to 75) at 7 1/2 to 8 1/2 whorls; ranging from rather thin- to thick-shelled. Shape: moderately depressed cone-shaped, with whorls somewhat in¬flated (especially on upper side); umbilicus wide (UD ca. 33% of SD). Sculpture: Upper side: SSR distinctly separated; LMR wider than UMR (usually ca. 2:1); ± wide groove at the base of LMR (in this groove often one additional fine spiral rib); fine nodulose sculpture of upper side due to many axial grooves (often > 100 per whorl on 5th to 7th whorl); Periphery: PR strong, often with 1 additional fine spiral rib between UPR and LPR; upper point of whorl attachment usually above LPR (thereby covering it; suture narrow); upper side and periphery crossed by deeply incised oblique axial grooves, resulting in formation of many elongate oblique segments, becoming weaker or smooth on MR-areas of body whorl of larger specimens; segments of the two midribs not necessarily corresponding; Base: IPR strong; often one additional narrow spiral rib between LPR and IPR; BF without spiral ribs; with radiating plications (especially in younger specimens), stronger towards umbilicus; two distincdy separated nodulose spiral ribs (PUR and UC) surrounding umbilicus, with umbilical crenae strong and irregular on later whorls; columellar wall forming almost straight inner lip with plications for support of the columellar muscle, with deepest groove in umbilical crenae overhanging umbilicus; no spiral sculpture on umbilical side of wall. Coloration: SSR initially white, with pattern of brown blotches (ca. 12-20 per whorl, each 2-3 nodules wide), starting at about 2 1/2 Tw; UMR initially mauve-brown, turning tan as LMR after about 2 1/2 Tw; UPR, LPR and IPR whitish with brown blotches, (each about two nodules wide); BF flamed with greyish-brown; one spiral band of small brown blotches in front of PUR; PUR initially white, later variegated light- and dark-brown; UC whitish-brown with darker markings (lighter colored on body whorl of large specimens). - Protoconch (see Fig.41): large to very large (1.2-1.64, x = 1.45); distinctly heterostrophic; with weakly defined ridge or distinct anal-keel; yellowish-brown. - Operculum: as described for genus. - Radula: "ptenoglossate," with 28 long, recurved, prong-like teeth per row (14-0-14); the outer ones being shorter and forked with long, tapering subequal cusps.

Height, 10 mm; diameter, 33 mm. Shell: depressed-turbinate; solid; with five granular spirals on the last whorl; fawn, spirally banded with brown. Spire: six whorls; suture channeled. Sculpture: four beaded spirals on each whorl, the last with an additional spiral at the periphery. Aperture: subcircular; operculum large, flat, paucispiral externally and with a twisted central projection internally; umbilicus wide and deep, bordered by a crenulated ridge and a narrower beaded spiral. Color: fawn, spirally banded with two interrupted spirals
of dark brown on each whorl.
Specimens have been dredged from depths of 30 to 50 m on sandy substrates. Juveniles are occasionally found deep within the umbilicus (Anon., 1962a).
A. maxima occurs throughout the Indo-West Pacific.

Architectonica maxima is aptly named, since it attains (together with A. trochlearis and A. taylori) the largest shell size in this family. The species is easily recognized by its clearly subequal division of the midrib-area, which has a distinct groove at the base of the lower midrib. The closest form is A. stellata .

Geographical distribution: Indian Ocean to western and central Pacific (Society Islands). Records from Madagascar, Australia and New Zealand in need of verification.
Habitat: Sublittoral (most depth records between 10 and 165 m, rarely to 280 m), live records from 10-50 m, sandy and muddy substrates.