Holotype: Shell of medium size for the genus, surface glossy, banded with reddish brown, most intense in the subsutural area and below the periphery, rib surfaces and pillar whitish; aperture about 1/3 the length of the shell, suture moderately impressed, whorls weakly inflated, subsutural area not demarked. Protoconch of 2.5 smooth whorls, tip small, postnuclear whorls 9. Axial ribs 8 on early whorls, increasing to 10 on penultimate whorl, extending from suture to suture, flexed in the subsutural area, tending to be aligned from whorl to whorl during early stages, obsolete upon the pillar; back of last whorl with a slightly more prominent axial rib 1/4 turn back; spiral sculpture of numerous minute striae, visible under magnification. Sinus deep, U-shaped, not strongly projecting, bordered on the inside by curved parietal callus; lip edge thin, stromboid notch weak; anterior canal scarcely defined, notched, inner lip flush with the pillar. Height, 20.3, diameter, 6.3 mm.

Drillia sinuosa differs from the other Drillias in having a more highly polished surface, less projecting sinus, and a distinctive color pattern. The name is Latin, full of windings, with reference to the flexed axial ribbing.

East Pacific. Type Locality: Off southern coast of Isla Santa Cruz, Galapagos Islands, Ecuador.