Type locality (Fig. 1). Western Australia, northwestern Kimberley, Bonaparte Archipelago, Admiralty Gulf, Montesquieu Islands, Oliver Island, 14°05'42"S 125°44'30"E; KC-062 (leg. V. Kessner & A. Longbottom, 18 June 1988).
Type material. Holotype WAM S34604 (Pl. 1.8). Paratypes WAM S41488 (3 preserved specimens), FMNH 219253 (3 preserved specimens).
Additional, non-type material. AMS C463727, FMNH 219250, WAM S41487 (Western Australia, northwestern Kimberley, Bonaparte Archipelago, Admiralty Gulf, Montesquieu Islands, unnamed island SE of Oliver Island, 14°05'55"S 125°44'50"E; KC-061).
Etymology. Named in honour of Norman L. McKenzie, Western Australian Department of Environment and Conservation, in recognition of his promotion of malacological research in Western Australia.
Sealing strategy. Rock sealer.
Shell (Fig. 17A–C, Pl. 1.8–9). Broadly conical to almost flat with low to medium spire. Thin to solid, translucent. Periphery rounded. Umbilicus concealed by columellar reflection to 50–100 percent, forming a chink or narrowly winding opening. Background colour brownish horn, ventrally lighter; with diffuse to well marked, thin, yellowish brown sub-sutural and mid-whorl bands that are most conspicuous on last whorl; outer lip colour same as shell; inner lip translucent, whitish. Protoconch c. 2.2 mm in diameter with 1.5 whorls, sculptured by strong axial elements. Teleoconch with coarse axial lirae; curved when viewed from above; rounded in cross-section with irregular spacing; spaces equal to thickness of lirae; distributed evenly across shell and across whorl diameter, reduced underneath suture. Angle of aperture 30°; outer lip rounded, sharp to moderately thick, slightly expanded, not or slightly reflected; basal node absent or weak; palatal node absent. Parietal wall of inner lip inconspicuous.
Pallial morphology. Pallial cavity short, extending half whorl. Mantle pigmentation consists of blackish spots. Kidney extending more than half of pallial cavity.
Genital morphology (Figs. 15–16). Penis straight, slightly longer than anterior part of oviduct. Vas deferens forms simple loop before entering penis. Penial retractor muscle shorter than penis. Penial verge very short (barely visible) to short (< 1 ⁄ 8 penial chamber), slender to spatulate with pointed tip. Penial wall pustules small, arranged in rows over entire length of inner penial wall. Main stimulatory pilaster welldifferentiated, relatively thin, cone-shaped, sculptured by ridges with little hooks, on apical portion of inner penial wall. Vas deferens rather straight to undulated, rather thick, entering penial sheath in upper third of penis. Vagina rather thick, tubular to posteriorly inflated. Inner vaginal wall with smooth longitudinal pilasters. Spermathecal duct wide, with smooth longitudinal pilasters inside. Spermathecal head globular to elongately inflated, connected with oviduct by connective tissue; inside entirely smooth with thin wall. Free oviduct more or less straight comprising less than half to about half of length anterior part of oviduct of anterior part of oviduct. Spermoviduct of same length as anterior part of oviduct. Talon embedded in albumen gland at junction with spermoviduct.
Radular morphology (Fig. 17E–F). Rectangular. Tooth formula C+12–18+2–3+18–20. With in average 135±12.5 rows of teeth, 31.2±1.2 rows per mm (n = 2). Central teeth with sharply pointed, triangular mesocones, shorter than base of tooth; ectocones vestigial. Lateral teeth with sharply pointed, triangular mesocones, length equal to base of tooth; ectocones tiny, endocones vestigial. Marginal teeth with triangular to ovate mesocones; ectocones shorter and narrower than mesocones; endocones reduced in size.
Comparative remarks. The studied museum material was labelled as “ Amplirhagada sp. 72” by Solem. This species is closely related to A. montesquieuana (see below) and A. combeana, both inhabiting islands in relative proximity. Amplirhagada combeana is similar in exhibiting a relatively pronounced but irregular axial sculpture but differs in having smaller main stimulatory pilaster, penial verge and no penial wall pustules.