Shell subglobose, 18.1-23.2 mm in height, 26.2-30.3 mm in width. Spire moderately to strongly elevated. Last teleoconch whorl slightly angulated. Shell dark brown to black, without umbilical patch, subsutural or supraperipheral bands. Aperture roundly ovate, height 12.6-14.7 mm, width 16.6-19.8 mm. Total number of whorls 5.6-6.0. Last teleoconch whorl with slight angulation; height 15.7-18.4 mm. Teleoconch sculpture of growth lines. Teleoconch periostracal sculpture of strong zigzag ridges with smaller ridges between major ridges. Protoconch sculpture pustulose. Shell uniform light to dark brown, without umbilical patch, subsutural or supraperipheral bands. Inner lip pale pink to pale mauve; strongly reflected and obscuring umbilical depression. Outer lip moderately deflected below midline of last whorl. Umbilicus closed.
Dimensions of types: Syntypes of Helix monacha (2), SH—22.2-23.2 mm, SW—26.0-30.3 mm, AH—13.0-14.2 mm, AW—16.6-19.5 mm, BW—17.6-18.5 mm, TW—5.75 whorls;
Non-genital Anatomy. Animal grey to dark grey, mantle dark yellow or orange. Kidney approximately 50-59% of length of mantle roof.

Pommerhelix monacha is most similar to P. duralensis but is larger and has a taller spire. This species exhibits a range of variation in size and shape, with larger specimens typically found in the wetter vegetation communities on the basaltic soils such as those that occur on the upper slopes in the Mt Wilson area, while the ones from the surrounding drier sandstone based soils are generally smaller. The observed anatomical and morphological variation and preliminary allozyme and 16S mitochondrial DNA data (Clark 2005) suggest that there may be additional unrecognised taxa.
Pommerhelix monacha, like most members of the genus, is relatively uncommon and sparsely distributed.

Pommerhelix monacha is found in the Blue Mountains, west of Sydney, in moist forests under wood, logs, rubbish and in leaf litter. Pommerhelix monacha appears to be relatively uncommon throughout its known range.