Phenacolepas senta: Shell cap shaped, with a protuberant and overhanging posterior apex, the earlier portion thin and translucent, the older solid and opaque ; adult shell asymmetrical by reason of a slight spiral twist. Colour white. The nepionic shell is very smooth and glossy sharply contrasting with the dull surface of the remainder, depressedly turbinate, apparently two whorled but swallowed past the nucleus by the older shell. Sculpture:—on the part next the nepionic shell there are circular growth lines, as these diverge wider their interstices are crossed by longitudinal lines which develop later into low small rounded ribs parted by slight furrows, these are reticulated by two series of fine raised threads crossing at right angles. Upon these ribs arise in quincunx order a series of V-shaped thorns, the limbs of which are directed anteriorly. A portion of the dorsal surface immediately above the posterior base is selected in the accompanying figure for illustrating this feature. Finally the limbs increase till they meet those of their neighbours and enclose a rhomboidal space, thus the marginal part of the shell becomes cancellated by a raised network, oblique both to the line of growth, the axis of the shell and the earlier sculpture. The minute transverse thread lines persist to the aperture.
Aperture subcircular, the edge when adult is broadened and finely crenulated. Interior glossy, the exterior sculpture visible through the shell. Muscular impressions are a right and left adductor scar and a narrow horse shoe marking the head line a little within the lip. Length 6, breadth 4,5, height 3 mm.
Eight empty shells from sand on the beach of Funafuti lagoon.