Shell minute, broadly ovate, yellowish white. Nuclear whorls one and one-half, well rounded, smooth. Post-nuclear whorls inflated, weakly shouldered on the posterior fourth between the sutures, marked by numerous slender rather closely spaced well rounded slightly protractive axial ribs, of which 20 occur upon the first, 24 upon the second, and 28 upon the penultimate whorl. In addition to the axial sculpture, the whorls are marked by slender spiral threads which are almost equal to the axial ribs. Of these threads, three occur upon the first and second whorl, dividing the space between the sutures into four almost equal portions, the space at the summit being a little wider than the rest; the first spiral thread marks the termination of the sloping shoulder. On the penultimate whorl an additional spiral cord makes its appearance in the space immediately below the summit, a little nearer to the summit than the first spiral cord on the previous whorl. The intersections of the axial ribs and the spiral cords form slender rounded tubercles. The spaces inclosed between the three cords on the early whorls and the same on the last turn are squarish pits, while the spaces between the summit and the first spiral cord and the axial ribs on the first two turns are rectangular pits, having their long axes parallel
with the axial sculpture. On the last whorl an additional spiral cord renders the pits between this cord and the next spiral cord and the axial ribs also squarish. Suture strongly constricted. Periphery of the last whorl marked by a sulcus as wide as that separating the suprasutural cord from the one adjacent to it anteriorly. Base well rounded, strongly umbilicated, marked by four equal and almost equally spaced spiral cords, which are as strong as those occurring between the sutures and the feeble continuations of the axial ribs. Aperture subcircular; outer lip thickened all around by a very thick varix; inner lip stout, decidedly curved, somewhat reflected over and appressed to the base; parietal wall covered with a very thick callus, which renders the peritreme complete.
The type and another specimen (Cat. No. 213699, U.S.N.M.) come from San Pedro, California. The type has three post-nuclear whorls, and measures: Length 1.6 mm., diameter 1.05 mm. Cat. No. 152193a, U.S.N.M., contains one specimen from San Pedro, California; and Cat. No. 226454, U.S.N.M., two from 3 fathoms, off South Coronado Island. Ten more from the same locality are in Doctor Baker's collection.
Named for Mrs. T. S. Oldroyd.