As O. mazatlanica:
Shell small, slender, white, the porcellanous layer subtranslucent, the surface layer very thin opaque white; nucleus smooth, of about a whorl and a half, blunt, and followed by five or six sculptured whorls which become more and more rounded and constricted in front of the suture; suture distinct, with (on the last whorl 20) small milk-white points coronating it and separated by small pits corresponding to the interspaces between the ribs; whorls smooth, or with obsolete indications of arcuate ribs which show by their more opaque whiteness faintly against the translucent under layer; basal disk hardly perceptible, not angulating the whorl, but trace- able by the row of faint indentations which bound the obsolete margin; surface originally covered with a microscopic reticulation of revolving and vertical lines impressed on a very thin chalky layer; base produced; aperture simple, surrounded by a thick white callous margin, the opening obovate. Height of shell, 12; of last whorl, 6; of peritreme, 3.5; maximum diameter, 4.0 mm. Type. Cat. No. 168669, U.S.N.M. Mazatlan, Mexico. The type-specimen is somewhat worn and polished, but shows the minute sculpture in sheltered places.