Shell to 33.6 mm SL; average adult size 29.49 mm SL (n = 14), of seven whorls, fusiform in shape with tall spire and inflated body whorl. Protoconch broken in all material examined; smooth, approximately 2 whorls. No varix apparently present, though beginning of first teleoconch whorl worn in all material examined. First teleoconch whorls bear ten broad axial ribs with interstices wider than ribs.
Five major spiral cords on first whorls, forming ridges that override and splay on top of axial ribs. Two minor cords appear between major cords starting on penultimate whorl and onto body whorl.
Suture adpressed, with no resorbtion or similar bonding at point where suture overrides sculpture of preceding whorl. Axial microsculpture of dense, fine growth lines over entire teleoconch.
Aperture strongly pinched at anterior terminus. Profile of outer lip smoothly curved. Neck short and stout, varying in length. Labral wall of aperture bears distinctive strong spiral lirae that terminate as row of 11-12 pale ridges some way behind lip, present up to terminus of suture; position of lirae not related to crenulations in lip, which reflect termini of spiral cords on outer face. Lirae do not run entire length of shell interior. Lip margin thin, corrugated, but lacking dentition. Parietal wall of aperture smooth, with some resorbtion of spiral sculpture; two short added spiral lirae present at anterior end in adult specimens. Labral margin smooth, except where thickening produces distinct margin in anterior third of canal. Canal broad, open, short and slightly reflected.
Shell pale to medium brown overall, with random dark axial patches.
Operculum thin, medium to dark brown with nucleus at anterior terminus.
Animal: Head small, with short, triangular lappets bridged by narrow web. Eyes at middle of outer margin of lappets. Large penis on right side anterior to head. Foot relatively smaller than in other members of genus; upper surface smooth. Proboscis long, very narrow.
Radula: Three teeth per row. Arcuate rachidian tooth bears three asymmetrical cusps; laterals simple, sickle-shaped with prominent sharp termini.
Remarks: Comparison of the radula of specimens identified as L. fuscolabiatum and Fusus modestus in the ANSP collection confirms them to be the same species. The degree of variation is less than that seen within a single L. musculus radula .

L. fuscolabiatum is known on the Pacific coast of Japan from Hakodate Bay in southeastern Hokkaido to at least Tosa Bay in southern Shikoku and from southern Korea (Gangwon and Gyeongsang Provinces: Min et al., 2006). Records from the Japan Sea are mostly from the area between Otaru on the western coast and the Oga Peninsula in Akita Prefecture, Honshu. Records from further south are sparse, but this species was recorded from the Noto Peninsula on the central Japan Sea coast by Amano & Vermeij (2003). Three possibly fossil specimens are in the NSMT collections from off the Noto Peninsula (NSMT-Mo 435556, R6240) and off the Oki Islands (NSMT-Mo 43559).