“Lepton parasiticum, n.s.
Mus. No. 11907.
Shell small, elongate ovate, inflated, thin; beaks nearly central, not prominent, surface shining, but not polished, with the texture of a Pandora. Shell white, hardly sculptured, but under a high magnifying power showing delicate concentric lines and fine radiating, apparently pubescent, lines extending from the umbones. Margins of the shell covered by an extension of the mantle, provided on each side with seven or eight stout cirri or tentacular processes. A single larger cirrus above the foot at the anterior end. Siphon short, foot small, very close to the anterior end of the shell.
Length, 2mm; height, 1.6mm.
Habitat, in the channels leading to the oral aperture of a species of echinoid (Tripylus), where it appears to lead a parasitic or at least a commensal existence. These echini were dredged by Dr. Kidder at Royal Sound, Kerguelen Island, near the station of the United States observers, in five and twelve fathoms. These tiny mollusks were quite abundant on the particular portion of the echinus mentioned, but none were found on any other part. It would seem as if the soft parts, before becoming contracted by the alcohol, must have almost entirely enveloped the shell. The latter was of such extreme tenuity that all efforts to remove it entire from the specimens resulted in its destruction. The teeth appeared, however, to resemble those of the other species of the genus; none of which, so far as I can recall, have been reported as commensal animals.”