Shell very small (to 7.1 mm in total length), smooth and glossy, fusiform, anterior truncated, with up to about 7,5 convex whorls, the last about 59% of total shell length; whorls sculpted with swollen ribs whose peripheries are near mid-whorl. Aperture short, oval, with a short and wide but distinctly formed anterior canal. Protoconch 1,5-1,75 smooth, translucent round whorls, the first partially immersed in the second, giving the apex a blunt appearance. Axial sculpture of large swollen ribs, wider than their interspaces, 10 on first teleoconch whorl, 7-10 on penultimate, and 4-7 on last to varix. Ribs extend from suture-to-suture on spire whorls, to anterior fasciole on shell base; only slightly narrowed and recurved in the sulcal region. Varix like an expanded rib, about twice the width of preceding ribs, 1/4-1/3-turn from the edge of the outer lip. Spiral sculpture lacking altogether. Sulcus absent; ribs and faint growth striae recurved below suture mark previous positions of anal sinus. Outer lip thin, translucent, surface with a single axial fold; lip edge bent slightly into aperture; stromboid notch lacking in examined specimens. Anal sinus deep, U-shaped, sides slightly divergent. Inner lip thin, recumbent, moderately wide, thin on parietal wall, and formed into a callus posteriorly, at the anal sinus. Anterior canal short but distinctly formed; unnotched; fasciole not swollen. End bent slightly to the right when viewed ventrally. Color uniformly light yellowish brown to off-white or pinkish with ribs and varix creamy yellow in some specimens.

Lissodrillia robusta has all the shell characteristics unique to Lissodrillia: a small glossy shell with ribs that extend from suture-to-suture, an anal notch with a divergent outer edge, a short anterior canal, and no spiral sculpture. Variability. The 62 specimens have an average total length of 4.72 mm (3.3-7.1 mm) and average W/L ratio of 0.409. There appears to be a latitudinal influence in shell color—the most northerly specimens, represented by the type series, are opaque and a light yellowish brown, while the more southerly ones from off Tampa and the Florida keys are lighter, partially translucent, and may also be off-white or pinkish. Identification. Lissodrillia robusta is similar to L. schroederi (Bartsch & Rehder, 1939), L. simpsoni (Dall, 1887), L. turgida, new species, and L. lactea, new species. From L. schroederi it differs in having rounder whorls, more bulging ribs, a varix positioned closer to the lip edge, and a rounder shell base. The last whorl is proportionately greater, 59 versus 55% of total shell length. Lissodrillia robusta differs from L simpsoni and L. lactea in much the same manner—rounder whorls and more bulging ribs. From L. turgida it differs in lacking square shoulders, and its whorls are not as convex, but it possesses more inflated ribs.

Type locality. Sackett Bank, offshore Louisiana, in 60-91 m.
Range and habitat. Louisiana (offshore); Mississippi (offshore); Alabama (offshore); W Florida (off Bay Co.; off Pinellas Co.; off Hillsborough Co.); Florida Keys (west of Dry Tortugas). Reported from offshore soft bottoms at 37-457 m depths.