Gyrineum lacunatum is the most widespread, most Common, and most variable species of Gyrineum. and so has received many synonyms. It is also the most common of the shallow-water tonnoideans studied here in the New Caledonian region, occurring in 186 samples. While all specimens are united by their small size (rarely exceeding 20 mm in height), their turbiniform protoconch of 1.8 to (more usually) 2.2 whorls (but ranging to as many as 2.6 whorls), their strongly cancellate sculpture on early spire whorls, their short, rapidly contracted last whorl and short anterior canal, and their pale pinkish lilac to deep violet aperture, the sculpture of intervariceal intervals of the last two whorls and the coloration are extremely variable. All specimens have even, cancellate sculpture on the early spire whorls, but as the shell grows the sculpture can cither remain coarsely cancellate, or the axial costae can fuse together into larger ridges, or become low and weak, eventually fading out altogether on the last one or two intervariceal intervals of some specimens. The spiral sculpture varies in the same way. on some specimens independently of the axial sculpture or, on others, concomitantly with it. In most specimens on which the sculpture becomes subdued over the last few intervariceal spaces, the colour pattern also fades out. so the exterior is uniform white. The end result in many samples {e.g. the many large collections of immature specimens, up to ca 10 mm long, that many museums have recently acquired from "deep-water shell debris" from the Philippine Islands) is a dimorphic population consisting either of cancellate. brightly banded pink, white and brown shells, or almost smooth (with subdued spiral cords and, on most shells, 2-3 low, smooth, widely spaced axial costae in each intervariceal interval), white shells in which the purple aperture provides the only obvious colour.

The distribution Of Gyrineum lacunatum almost coincides with the limits of the tropical Indo-West Pacific faunal province, i.e. it occurs throughout the Indian and western Pacific Oceans (but not in the Red Sea, where it is replaced by the similar G. concinnum). In the Indian Ocean, it ranges from Port Alfred, South Africa (NMP D2188; 19 other lots from South Africa and Mozambique examined on loan from Natal Museum), through the oceanic islands (Mauritius and Reunion; DRIVAS & JAY, 1988: 66; also material examined in MNHN and NZGS), along the entire East African coast, to Oman (NZGS WM13167. Masirah I., pres. E. & D. Bosch), then eastward to Hawaii (KAY, 1979: 226) (“Oahu" [but probably really from Kauai], type locality of Triton lacunatum: JOHNSON. 1949: 217, 226). The southern limit seems to be near Sydney. New South Wales (Sydney Harbour "Triton" dredgings. Captain Comtesse, holotype of Apollon facetus. + one other specimen in AMS; Botany Heads, New South Wales, ex Hargreaves Colin (I AMS CI47607); Cape Banks. New South Wales, i.e. Kumell headland, S. Botany Bay, 1 AMS); a single specimen has been seen from Lord Howe Island, southwest Pacific (AMS C59464) and, of course, taken abundantly around New Caledonia. The northern limit in Japan is the Izu Peninsula, Honshu

BRODERIP'S (1833a) type specimens of Gyrineum pusillum are a white species of Gyrineum with a distinctive protoconch of only 0.8 whorls. They are not conspecific with the multicoloured, variably sculptured species with a protoconch of 1.8-2.2 whorls that has borne this name since the highly influential works of G.B. SOWERBY II (1835-1836) and REEVE (1844b) incorrectly illustrated G. lacunatum under the name Ranella pusilla. As BRODERIP (1833a: 194) clearly described Ranella pusilla as "alba", the approach taken here has been to designate one of Broderip's undoubted white syntypes as the lectotype of Ranella pusilla. and adopt Gyrineum lacunatum for the multicoloured species more usually known by this name, in preference to applying Broderip's name to one of his more doubtfully associated syntypes(?) and proposing a new species name for the white species.