Shell small, slender, acute, solid, finely reticulate, imperforate, with seven and a half normal and three and a half thin, translucent, smooth, shining, nuclear whorls; spiral sculpture of twelve to fifteen flattened crowded threads, a broader one marginating the anterior edge of the suture to which it is closely appressed; these cross (on the last whorl 9-10) rather angular transverse ribs, which on the last whorl are a little elbowed on the periphery, but in general are pretty even, becoming obsolete toward the sutures. The spiral threads are crossed by a multitude of extremely fine, rather even sharply defined lirae, which extend from suture to suture, neatly reticulating the spiral sculpture, and giving to the extremely narrow interspaces a punctate aspect; there are very few varices on the shell; in the type the last whorl begins and ends with one; the aperture is nearly circular, with a groove around its inner margin, outside of which is the cancellated anterior face of the very thick varix, which is somewhat excavated behind; base rounded without carina or special sculpture. Lon. of shell, 6.87 mm; of last whorl, 2.5 mm; of aperture, 1.25 mm; max. lat. of last whorl, 2.0 mm.

Adult reaching about 10 mm. ( 0,5 inch) in length, attenuated, imperforate, and sculptured. Whorls 10-12, moderately convex. Nuclear whorls 2,5, smooth, amber in color. Color a uniform grayish-white. Suture finely crenulated and not deeply impressed. Aperture oblique, subcircular to ovate. Outer lip much thickened and rounded. Columella short and arched. Axial sculpture consisting of numerous costae each of which ends as a crenulation in the suture above. There are 14-10 costae on the body whorl. These costae are rounded over the convex whorl. There may be 2 or 3 varices on the adult shell. Microscopic sculpture consisting of exceedingly fine punctated or pitted spiral lines. No basal ridge defined. Operculum unknown.

Remarks. This is an exceedingly variable species, particularly in the contour of the shell, the costae and the whorl angulation. Dall considered these West Indian forms to be varieties of Opalia helleniea Forbes from the Mediterranean. This certainly may be so but the lack of critical material and some differences in the description of that species make it advisable to keep these forms separated at least for the time being. Certain of the above synonyms have been based upon young specimens. This is easily done as Opalia produces a well defined lip during its early period and as the shell advances in age a new growth proceeds until another or even a third varix is produced.
Opalia pumilio differs from morchiana by having rounded instead of angulated whorls and having, in general, smaller and more numerous costae.

Atlantic. From Caribic to East Atlantic. Barbados.
Range. North Carolina, the Gulf of Mexico and south through the West Indies.