[3] Dall & Bartsch made the distinction based upon the length of the adult shell (O. donilla 4.5 mm and O. gravida 6.5 mm) and the incised spiral lines moderately strong in O. donilla, but exceedingly fine in O. gravida.

The nuclear whorls are deeply obliquely immersed in the first of the succeeding turns, above which only the tilted edge of the last volution projects.

The six post-nuclear whorls are well rounded, slightly contracted at the suture and appressed at the summit.

The base of the shell is slightly rounded, sloping abruptly from the periphery to the umbilical area.

The entire surface of the base and the spire is marked by numerous almost vertical lines of growth and many well-incised spiral striations.