Diagnosis
Shell subglobose, 25.5-33.2 mm in height and 30.9-38.7 mm in width. Shell pale yellow to tan, with red umbilical patch and narrow red subsutural band. Mantle reddish orange. Penis very long and about equal in length to vagina. Verge short to elongated. Albumen gland small.
Description
Shell : Subglobose, 25.5-33.2 mm in height, 30.9-38.7 mm in width. Spire moderately elevated. Aperture roundly ovate, height 16.3-21.2 mm, width 18.5-24.7 mm. Total number of whorls 5.6-6.0. Last teleoconch whorl rounded; height 20.2-27.6 mm. Teleoconch sculpture of growth lines. Teleoconch periostracal sculpture of weak zigzag ridges with minor sculpture between major ridges. Protoconch sculpture weakly pustulose. Shell yellow to tan, with broad red umbilical patch and narrow to broad red subsutural band, and sometimes with an additional red supraperipheral band. Some specimens are very dark but still retain evidence of the red bands. Inner lip pale pink to pale mauve, strongly reflected and largely obscuring umbilical depression. Outer lip moderately deflected below midline of last whorl. Umbilicus closed. Dimensions of holotype: SH—26.7 mm, SW—35.9 mm, AH—17.5 mm, AW—23.1 mm, BW—22.5 mm, TW—5.70 whorls.
Non-genital Anatomy. Animal colour orange, mantle reddish orange. Kidney approximately 50-59% of length of mantle roof.

Meridolum marshalli is the largest species in the genus, and about the third largest camaenid found in New South Wales. It can be easily distinguished from other species in the genus by its large size and shell colour pattern, with individuals often appearing to be bicoloured. In the Bulli Pass area there appears to be a potential hybrid zone between M. marshalli and M. gulosum (personal observations), as some of the individuals in this area are the size and shape of M. gulosum but have a shell colour pattern more reminiscent of M. marshalli; this remains to be tested.

Meridolum marshalli McLauchlan, 1951 is restricted to the rainforests found from the Royal National Park at Audley south to about Bulli Pass, S. of Sydney. It is found under fallen Cabbage Palm [Livistona australis (Brown, 1810)] fronds and in leaf litter.