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 im¬pressed. 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.

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.

A half inch shell with 10-12 whorls, grayish white in color. Axial sculpture of 14-16 ribs on the body whorl. No basal ridge. Spiral angle is about 25 degrees although this varies somewhat. The small size of the shell makes it look more delicate than its description. Umbilicus hidden. Form morchiana differs by having more angulated whorls and fewer but larger costae. O. pumilio may be a western form of Opalia hellenica (Forbes, 1844). Dall described it as form nodosocarinata of that species in 1889. It ranges from North Carolina south through the Gulf of Mexico and West Indies.

North Carolina, the Gulf of Mexico and south through the West Indies.