MATERIAL EXAMINED: TAE Stns 79, 100; NZOI Stns A449, A470, A471; USNM 488933, off Cape Royds, Ross Island, McMurdo Sound, 106 m.
DISTRIBUTION: Known only from the Ross Sea in 67-377 m.
DESCRIPTION: Shell of medium size for the genus, tall in relation to diameter, fragile, white, spirally sculptured, narrowly umbilicate. Height of spire considerably greater than diameter (diameter/height ratio, 79-82). Whorls four, including protoconch of a single smooth bulbous whorl. Spire whorls somewhat inflated, contour of outline evenly rounded. Suture slightly impressed. Sculpture consisting of delicate slightly raised spiral threads that arc easily rubbed off leaving a smooth surface, so that the earlier spire whorls appear smooth on most specimens. On the last whorl, about 16 spiral threads between the suture and adapical margin of the aperture, spirals across the rest of last whorl and base vary in strength, about nine on the holotype. Area surrounding the umbilicus with finer, closely spaced spiral threads. Umbilicus a narrow chink, partly closed by the reflection of the columellar lip. Aperture subcircular with a somewhat squarish outline. Outer lip thin, sweeping backwards from junction with last whorl, basal section protruding at first, then curving backwards to junction with the columella. Columella straight, expanded at base and reflected slightly across last whorl. Parietal lip thin, junction with last whorl well back in aperture.
MEASUREMENTS: Height 2.4 mm, diameter 1.9 mm (holoptye); height 2.2 mm, diameter 1.8 mm (paratype).
REMARKS: L. macknighti differs from S. notalis Strebel from South Georgia in its higher spire, its more swollen whorl outline, its more prominent spiral sculpture and its narrower umbilicus. It has a more elevated spire than either Lapidicola gyratum Egorova, 1972 or Intortia homocostata Egorova, 1972. As Egorova's work has shown, anatomical study of these small, relatively featureless gastropods may well show that several generic groups are present.