Trochoid-turbiniform, moderately elevated (L/D=l .10-1.25); teleoconch of up to 6.5 whorls; spire whorls somewhat flat-sided; suture strongly indented, inserted at level of subperipheral cord and thus appearing somewhat channelled, descending slightly just prior to outer lip. First teleoconch whorls sculptured with curved axial pliculae; 2-3 spiral cords arise during second whorl, and additional ones with subsequent growth; penultimate whorl with approx. 5 well developed cords, a sixth level with suture; subsutural cord strongest, but becoming distinctly weaker just behind outer lip; cords equal to or narrower than their intervals. Axial pliculae of first whorl persist on later whorls producing a distinct cancellation and rendering spiral cords granular where they cross them; granules of subsutural cord usually largest, becoming smaller and more numerous toward periphery; interstices more or less square on spire whorls, becoming axially elongate on last adult whorl, particularly so just behind outer lip. Base similarly sculptured with approx. 6 spiral cords, the last of which forms umbilical margin; umbilicus remaining open at maturity (very occasionally almost occluded by reflected columella). Peristome oblique; aperture D-shaped, flattened parietally; columella thickened, bearing a low bulge in the mid region and a well-developed, peg-like tooth basally; a deep U-shaped notch separates basal columella tooth from first denticle of basal lip; parietal callus not extending far beyond aperture, bearing spiral ridges; margin of outer lip somewhat flaring, the edge finely and rather irregularly crenulate; interior of outer lip with a subterminal thickening which is set with relatively strong, inrunning, ridge-like denticles, these become weaker toward lip margin and develop finer intermediaries (at maximal maturity); denticles not extending far into aperture, one nearest basal columella notch usually larger; 1 or 2 small rounded granules may be present on columella near bottom of basal columella notch; interior of aperture nacreous; exterior of outer lip sometimes with a broad low subterminal thickening, but lacking a rib-like varix. Microsculpture: Juvenile shell with vermiform spiral threads; later whorls with close-set, scratch-like marks beneath intritacalx. Protoconch: White, more or less level with first teleoconch whorl or at most weakly exsert, with a weak apical beak; diameter 220-240 µm; terminal lip distinctly convex; superficial sculpture well developed, arranged in irregular axial lines, with a weak spiral element. Colour: White to yellowish white, later whorls with reddish to brown spots, blotches or axial flames; markings generally browner in fresh specimens; a white to dirty brown intritacalx is present in fresh specimens but this is worn off in most museum material. Shell surface often encrusted by other marine organisms. Dimensions: Largest specimen seen, length 11.9 mm, diameter 10.0 mm (lectotype of Monodonta alveolata A. Adams, 1853). Operculum: Initially tightly multispiral, but whorls broadening with growth and becoming more openly multispiral.

The synonymy of Trochus instrictus Gould, 1849, Monodonta alveolata Adams, 1853 and M. bourcierei Crosse, 1863 has been noted previously on several occasions (e.g. Pilsbry 1890 in 1889-90; Cemohorsky 19786; Kaicher 1990). Other species with similar apertural dentition and umbilical form include H. crassilabrum (Sowerby, 1905) from Sri Lanka, H. exasperatum (A. Adams, 1853) from the Philippines, H. gemmatum (Gould, 1845) from Hawaii, and H. seychellarum (G. & H. Nevill, 1869). H. exasperatum and H. seychellarum, however, are much less elevated, whilst H. gemmatum and H. crassilabrum have more rounded whorls with relatively close-set and more obviously beaded spiral sculpture, the latter also has a more strongly developed upper columella denticle and a partially occluded umbilicus; all are smaller than H. instrictum. Amongst south-western Indian Ocean chilodontid taxa, only H. seychellarum retains a simple and deep umbilicus when mature, but that species is considerably smaller and more depressed.

Indo-West Pacific; from southern Japan, SE Asia and the south-western Pacific to western Australia, the Andaman Islands and East Africa; in the western Indian Ocean extending south to southern Madagascar, but not yet recorded from central or southern Mozambique, or South Africa. Recorded from Quaternary deposits in the Marshall Islands (Ladd 1966). Little information regarding the habitat oi living animals is available. Adams (18646) reported a living specimen dredged at 55 fath. [-100 m] off southern Japan, but most of the specimens available (live and dead collected) have come from near-shore reef systems with a coralline facies (AMS and WAM material). Wilson (1993) gave the bathymetric distribution as intertidal to -140 m. but did not specify whether this concerned living or dead material. Sasaki (2000) cited the habitat as intertidal and upper subtidal, on coral rubble, and in northern Mozambique. J. Rosado has collected it alive amongst dead coral in the shallow subtidal.