Archaeostylus

Archaeostylus manukauensis has a large 60.2–70.4 millimetres or 2.37–2.77 inches long shell that is thin, elongate-conical, and slightly dorso-ventrally compressed.^[1] Unlike other genera of flax snail, A. manukauensis lacks a thickened outer lip surrounding its aperture, and instead possesses a thin peristome with a collabral callus ridge on the palatal wall. In all of the specimens studied, a broad, shelf-like callus ridge extends from top of aperture almost to the base of the columella, bearing a flattened, irregularly rounded, tongue-like projection on its upper part.

Fossils of this extinct land snail species are known only from the Late Pliocene/Waipipian (~3.6–3.0 Ma) Māngere Shellbed, located approximately 30 m below the suburb of Mangere, Auckland.^[3][1][4] It is currently regarded as one of the two oldest known flax snails species represented in the fossil record, along with a single specimen of another species (Maoristylus pliocenica) also from the Māngere Shellbed.^[1] A. manukauensis presumably inhabited lowland broadleaf forest and scrub habitats, similar to recent species of flax snail.^[5] Its buoyant shells likely ended up in marine shellbed deposits after being washed to the coast in streams, or in run-off after heavy rainfall.