Shell small, subplanispiral, heterostrophic, densely coiled and covered by a thin, colourless periostracum and thick ferrugineous deposits. The protoconch consists of about 1.4 smooth whorls, diameter 275 µm, with a very small initial part and is distinctly hyperstrophic. There is no sharp demarcation between protoconch 1 and 2. The teleoconch of the holotype consists of 3.25 whorls of an indistinctly hexagonal cross-section, separated by a deep, channelled suture. The periphery is indistinctly angulated and forms a blunt keel. The whorls are attached to the preceding whorl just below the periphery of this whorl, so the coiling is not perfectly planispiral. At the attachment zone the periostracum is double and between these layers are ferrugineous deposits, so when these are removed, the coiling becomes disjunct. The whorls overlap about one-sixth of the preceding whorl, and the profile of the outer lip is distinctly sigmoid. Dimensions. Diameter of holotype 3.88 mm. Radula :Typical for the genus, short and broad with about 33 transverse rows of teeth. The shape of the teeth seems to be very similar to the type species, but the teeth have more numerous cusps. Operculum. Round, thin, colourless and multispiral.

Xylodiscula major is twice as large as any other species known of the genus. It is also proportionally flatter, although the small, decalcified specimen shows that at a size of 1.2 mm the proportions are similar to the other described species.