Amastra subrostrata was an extinct species of air-breathing land snail, a terrestrial pulmonate gastropod mollusc in the family Amastridae.

[3] The length of the shell attains 15 mm, its diameter 8 mm The shell is imperforate, dextral, ovate-conic, and solid, with an irregularly striate surface that is slightly glossy.

Its coloration is brown, irregularly clouded with tawny hues.

The spire is swollen-conic with a rather acute apex and consists of six whorls.

The aperture is slightly oblique and irregularly semi-elliptical, angular at the columella, giving it a beak-like extension.