Amastra mucronata is a species of air-breathing land snails, terrestrial pulmonate gastropod mollusks in the family Amastridae.
The length of the shell attains 17.5 mm, its diameter 8 mm.
The shell is dextral, elongate-ovate, and predominantly white, adorned with numerous transverse arrow-headed brown markings. The body whorl, however, is cloaked in a dense, brownish-black epidermis. It is composed of six rounded whorls, with the last one slightly contracted.
The suture is subtly impressed on the upper whorls, becoming more pronounced at the junction with the body whorl. The aperture is small and ovate, while the columella features a distinct twisted plait. The outer lip is simple and unembellished.
This species is endemic to Hawai, occurring on Molokai island.