Plesiocystiscus is a genus of minute predatory sea snails, marine gastropod molluscs or micromolluscs in the family Cystiscidae.

Suture rapidly descending on last half of last whorl, then abruptly sweeping upward just before lip, giving characteristic shape to adult shell.

Lip thin anteriorly, gradually thickening tower shoulder, smooth, lacking denticulation or lirae, external varix absent.

The radular and shell features, including the presence of odontophoral cartilage hoods, possession of cystiscid internal whorls, and lack of an external varix, place this group in the Cystiscidae.

This genus is found in the Eocene of France, the Miocene and Pliocene of Florida, and the Pleistocene of California, to the Recent.