Type species: Mitra sulcata Swainson in Sowerby, 1825.
Shell moderately small, up to 30.0 mm in length, solid, almost biconic, fusiform-elongate, teleoconch of 6-8 whorls, protoconch probably conical-multispiral. Sculptured with prominently angulate spiral cords, almost "V"-shaped interspaces and axial striae; aperture narrow, longer than the spire, smooth within, outer lip convex and fluted, columella narrowly calloused and with 3-5 oblique folds, siphonal notch distinct, siphonal canal straight. Periostracum moderately thin but opaque and brown in color. Radular ribbon extremely small, 0.73 mm long in a shell 20.0 mm in length, rachidian broadly rectangular and with 4 short, broad cusps, lateral ca. 5 times the width of rachidians and with ca. 24 sharp, not deeply rooted cusps.
The radula of the type species S. sulcata is so different to the radula of the group comprising the interlirata - erythrogramma group of species that they cannot all be combined under the genus Subcancilla. Other important features in the radula of Subcancilla are the very small size of the radular ribbon (sulcata = 3.6% of shell length and erythrogramma - 23% of shell length) and the minute size and different structure of the teeth (sulcata = 95 rows of teeth per 1.0 mm of ribbon-length and erythrogramma - only 13 rows of teeth per 1.0 mm of ribbon-length). The radula of S. sulcata resembles the radula of Mitra (Nebularia), but Subcancilla has been retained tentatively as a valid genus until the radulae of the type species of Cancilla and Ziba become known. The genus contains only one living W. American species which is found from the intertidal zone to beyond the littoral zone and one Caribbean fossil species. For further discussion see remarks under the interlirata-group of Ziba species.