Shell fusiform with an acute spire, nine whorls, and a globular brownish, shining, smooth nucleus of about two whorls ; shell with a polished surface over a straw-colored very thin outer layer, the only transverse sculpture being due to the faint incremental lines and irregularities of growth; spiral sculpture of an extremely sharp and wide keel nearer to the suture in front than to the one behind, and in some cases having its edge actually curved forward and overhanging; the margin of the keel is smooth and a little rounded; it is fainter on the last whorl of the adult; in front of the keel on the base is a slight angulation or hardly elevated thread on which the suture coils; in front of this are some faint spiral markings, hardly breaking the smoothness of the surface ; suture distinct; aperture narrow; notch deep, wide, extending from the suture nearly to the edge of the keel; outer lip thin, arched forward, not internally lirate ; pillar lip slightly excavated, white, smooth; pillar straight, attenuated in front, canal narrow, straight, shallow; base moderately rounded in the adult, flattish in the young; operculum as in L. tenoceras. Long. of shell, 30.0 mm; of last whorl, 20.3 mm; of aperture, 17.0 mm; max. lat. of shell, 11.0 mm.

None of the Challenger species approach this one. The Surcula staminea and S. gonioides of Watson are carinated, but the keel is far less pronounced than in the present species, and they do not appear to have that curious chalky outer layer like a coat of whitewash varnished, which is so peculiar in L. subgrundifera. In the last there is some variation in the strength of the basal spirals, but in none of them do the latter rise much above the surface.

Gulf of Mexico. Yucatan Strait. Florida and northward to North-Carolina.