What is "testacella"

Testacella is genus of small to medium-large, predatory, air-breathing, land slugs. They are terrestrial gastropod mollusks in the family Testacellidae, the shelled slugs. They are not often seen because they live underground.

Testacella is the only genus in the family, in other words it is a monotypic family. Testacella is the type genus of the family Testacellidae.