Northland east coast; Takou Bay. Widespread in the Indo-Pacific, from South Africa and the Red Sea to the Hawaiian Islands and Marquesas.
Shell with a low spire and a sharp peripheral angulation, composed of only one spiral keel, but with a few weak spiral grooves both above and below it. A heavy crenulated ridge borders the deep and relatively wide umbilicus. Colour yellowish-brown, blotched and spirally lined on a whitish ground; periphery alternately white and brownish blotched; umbilical margin pure white.
Height 10.0-10.5 mm., width 15.0-16.0 mm.
Architectonica radiata Roding, 1798, p. 79. Philippia manifesto Iredale, 1931, p. 229. Powell, 1938A, p. 168. P. (Psilaxis), Robertson, 1970, pp. 76, 77.

Small to large cone-shaped shell with rounded to prominently angulated peripheral keel and moderately wide umbilicus; whorls inflated, smooth and glossy; spiral sculpture restricted to three peripheral ribs (central one stronger and more prominent), and two ribs surrounding umbilicus (narrow proxumbical rib and wider umbilical crenae). Striped, flamed or mottled in shades of brown, usually lighter color pattern on periphery; umbilical crenae whitish. Protoconch diameter 1.16-1.52 mm; with long, sharply crested anal keel (< 0.34 mm); whitish without distinct pattern in center of last whorl.
Teleoconch: small to large, diameter of specimens in collections usually 7-22 at 2 1/2 to 5 1/4+ whorls. Shape: cone-shaped with rounded to prominently angulated peripheral keel, inflated whorls and moderately wide umbilicus (UD ca. 19% of SD). Sculpture: Upper side: ± smooth, SSR and MR not developed (weak nodulose sculpture on early whorls of some specimens, sometimes with indistinct spiral threads on later whorls); Periphery: ± prominent keel formed by strong LPR, with weaker UPR and IPR on either side; upper point of whorl attachment on LPR; Base: BF smooth (in small specimens with axial plications, stronger towards umbilicus); IPR and UC distinctly separated, UC much wider and bearing large nodules; columellar wall forming almost straight inner lip with plications for support of columellar muscle, with deepest groove in UC overhanging umbilicus; no spiral sculpture on umbilical side of wall. Coloration: highly variable, always in shades of brown; usually whitish with a wide brown subsutural band with ± regular axial flames extending over the upper side; these flames often fading into an irregularly mottled pattern; other specimens overall brown with a lighter-colored pattern at the periphery (see Fig.95); UC always whitish. - Protoconch: medium-sized to very large (1.16-1.52, x = 1.36), distinctly heterostrophic, with long, sharply crested anal keel (0.18-0.34, x = 0.27; see Fig.99); usually white, with anal keel and outer corner in front of varix brown. - Periostracum and Operculum: as described for genus (operculum figured by ROBERTSON, 1970). - Radula: five-toothed taenioglossate (2-1-2); rachidian with strong central cusp flanked on either side by a filiform cusp; inner and outer marginal teeth each with 5-6 long, filiform cusps (BIELER, 1988: 236; some teeth figured by ROBERTSON, 1970: 73, fig.9). - Jaws: consisting of elongated elements (ROBERTSON, 1970: 73, fig.7). - Anatomy: not studied. - Soft-body coloration of living animal: translucent white with solid-white granules embedded in head-foot except for sole of foot (pers. observ., South Africa).

(Synonyms: Torinia cingulum (Kiener) Sowerby, 1863; Philippia hybrida (Linnaeus) Tinker, 1952.) Height, 8 mm; diameter, 14 mm. Shell: as in P. oxytropis but distinguished by a smaller, white protoconch (1.20 to 1.45 mm in diameter) and, among the color patterns of the teleoconch, that which is white with brown subsutural bands and radial extensions (Robertson, 1970b).
These sundials are less numerous than P. oxytropis and occur from shallow water to depths of 50 m. The animals live buried 1 to 3.5 cm in silty sand or loose, algal-covered rubble near colonies of the coral Porites lobata Dana, the snails emerging at night and feeding on the polyps (Robertson and others, 1970). Metamorphosis of the veliger larvae is strongly influenced by the presence of the coral, Porites lobata, and growth of the teleoconch is apparently dependent on the presence of the coral (Hadfield, 1976). One animal reared in the laboratory began laying eggs at a shell diameter of 712 mm, less than three months after it had metamorphosed (Hadfield, 1976).
P. radiata ranges throughout the Indo-West Pacific from South Africa and the Red Sea to the Philippines, New Zealand, Micronesia, Polynesia, and the Marquesas (Robertson, 1970b).

The identity of Psilaxis radiatus has been a matter of dispute in the literature, especially because many authors have confused it with Philippia hybrida (LINNE, 1758); Ph. hybrida is the Mediterranean/Adantic "sibling" of Ph. lutea (see above). BAYER (1942) discussed the Recent Philippia (and Psilaxis) species extensively, and distinguished many different species and "varieties" in the complex now considered as the genus Psilaxis. ROBERTSON (1970: 66 ff.) critically revised that group and, in agreement with the present study, found it to consist of only three Recent species, Ps. radiatus and Ps. oxytropis ADAMS, 1855, in the Indo-Pacific, and Ps. krebsii (MORCH, 1875) in the Atlantic Ocean. The two Indo-Pacific species are very similar to each other, with Psilaxis radiatus usually having shells with a narrower umbilicus. "While white shells with brown subsutural bands and radial flames can be readily recognized as P. radiatus, it is necessary to study the protoconchs of specimens with other color patterns.

Subtropical and tropical Indian Ocean and western to central Pacific. Occasionally reported from eastern Pacific [Isla Gorgona, Colombia (ROBERTSON, 1979), Golfo de Veraguas, Panama (EMERSON, 1983, 1984) and Cabra Island, Panama (specimen in NMW)], but probably no brooding populations are established in that area (ROBERTSON, 1979: 192).