Shell very small (to 6.4 mm in total length), smooth and glossy, fusiform, anterior truncated, with up to 7,5 slightly convex whorls, the last about 56% of total shell length; sculpted with ribs whose peripheries are near the anterior suture such that whorls appear to be cinched, or to sag. Aperture short, oval, with a short and wide but distinctly formed anterior canal. Protoconch of 1,5-1,75 smooth, glossy, disproportionately large whorls, the first partially imbedded in the second such that the shell apex appears blunt. Axial sculpture of smooth, round-crested ribs that run from suture-to-suture on spire whorls, evanesce below whorl periphery on shell base; 9-11 on penultimate and 4-8 on last whorl to varix. Ribs are wider than intercostal space, recurved on whorl shoulder and otherwise straight on spire whorls and slightly opisthocline on last whorl. Growth striae microscopic, oblique to ribs and recurved on shoulder. Varix an enlarged rib, up to twice the width of preceding rib and positioned 1/3-1/4-turn from edge of outer lip. Spiral sculpture absent. Sulcus absent; recurved ribs and striae on whorl shoulder mark past positions of the sulcus. Outer lip thin, translucent except for an axial folds, usually one nearest edge of outer lip; edge of lip, together with anal sinus, traces a reversed "S" from anal sinus to anterior canal; stromboid notch absent, or very weak. Anal sinus a deep wide notch with a round apex near suture, outer side divergent from inner. Inner lip thin, margined, free on anterior canal, recumbent on parietal wall, formed into an elongate, weak callus at the posterior end of the aperture. Anterior canal short, open, unnotched; fasciole not swollen. Color light to dark golden brown with white or white with rose-tinted ribs. Specimens occur with white color on just the rib crest, entire rib, or a continuous band of white across ribs and intercostal space.

Lissodrillia simpsoni has all of the characteristics of the genus: a small glossy shell with ribs suture-to-suture on spire whorls without a sulcus; inner edge of anal sinus and outer lip trace a reverse "S"; and the lack of spiral sculpture. Variability. The average total length of 42 specimens is 5.69 mm (4.7-6.6 mm); their average W/L ratio is 0.391. Specimens from deeper water (73 m) are slightly smaller, almost entirely golden brown, have weaker ribs, and may represent a separate species. Identification. Lissodrillia simpsoni is similar to L. schroederi (Bartsch & Rehder, 1939), L. robusta, new species, L. lactea, new species, and L. levis, new species. From L. schroederi it differs in possessing straighter ribs, and in being a different color— white or pink versus golden brown. Confirmed lots of L. simpsoni have been reported from "shallow" water to 73 m, mostly under 50 m depths, while those of confirmed L. schroederi occur in 30-183 m depths, mostly over 50 m. So there seems to be bathymetric separation of these two similar species. From L. robusta it differs in being slimmer in form, lacking the bulging ribs that characterize L. robusta. This latter species is also uniformly colored, without a broad central band like that of L. simpsoni. From L. lactea it differs in possessing less convex whorls, usually more ribs (9-11 versus 6-10 on the penultimate whorl), and in being a golden brown, not white. From L. levis it differs in being somewhat smaller 5.69 versus 6.74 mm in average total length), having more distinct and narrower ribs, and in possessing a different coloration.

Type locality. Tampa Bay, Hillsborough Co., W Florida, in about 5 fms [9 m].
Range and habitat. W Florida (Okaloosa Co.; Bay Co.; Pinellas Co.; Hillsborough Co.). Dall (1889a: 91) states that specimens from off North Carolina (USFC Stations 2607 & 2619) are this species; however, this has not been confirmed and is considered unlikely. Reported from shallow water to 73 m.