Diagnosis
Shell subglobose, 20.5-23.1 mm in height and 24.5-28.5 mm in width. Shell pale yellow with red umbilical patch and narrow red subsutural band. Mantle reddish orange. Penis longer than vagina. Internal structure of upper penial chamber of inverted diamond shaped pustules.
Description : Shell subglobose, 20.5-23.1 mm in height, 24.5-28.5 mm in width. Spire moderately elevated. Aperture roundly ovate, height 12.1-15.7 mm, width 14.2-17.7 mm. Total number of whorls 5.4-5.8. Last teleoconch whorl rounded, with slight angulation; height 17.5-19.0 mm. Teleoconch sculpture of prominent growth lines and weak pustules. Teleoconch periostracal sculpture of weak zigzag sculpture with smaller ridges between major ridges. Protoconch sculpture weakly pustulose. Shell uniform yellow to light brown, with small red umbilical patch, and narrow red subsutural band; supraperipheral band absent. Inner lip pale pink to pale mauve, reflected and obscuring umbilical depression. Outer lip moderately deflected below midline of last whorl. Umbilicus closed. Dimensions of holotype: SH—21.5 mm, SW—24.5 mm, AH—12.1 mm, AW—14.2 mm, BW—17.5 mm, TW—5.25 whorls. Non-genital Anatomy. Animal and mantle reddish orange. Kidney approximately 50-59% of length of mantle roof.

Pommerhelix insularis n. sp. is easily distinguished from all other members of the genus by its relatively large, thin, pale shell and its very distinctive male genitalia with the internal penial sculpture consisting of overlapping diamond shaped pustules. Specimens very similar morphologically to Pommerhelix insularis have been found on nearby Boondelbah Island and Broughton Island 11 km further north. There is another population, which is morphologically similar but smaller in size, which appears to be restricted to a small area of vine thicket on the western side of Yacaaba Head on the northern side of Port Stephens. Further studies using anatomy and DNA will be required to determine the status of these populations.

Pommerhelix insularis is only known from the Cabbage Palm [Livistona australis (Brown, 1810)] grove on Cabbage Tree Island, off Port Stephens. Pommerhelix insularis is found in the leaf litter and under fallen palm fronds. The grove is also the primary breeding colony of the Gould's Petrel [Pterodroma leucoptera (Gould, 1844)].