2 species (see text) Barythaerus is a small genus of marine bivalve molluscs of the family Thraciidae.

[2][3] The genus is endemic to the waters off southern New Zealand.

Live specimens have been found from bryozoan and shell substrates at intermediate depths (55–183 m).

[1] There are two recognized species:[2] Barythaerus are small bivalves, with the larger species (Barythaerus cuneatus) reaching 5.5 mm (0.22 in) in length.

They resemble Parvithracia but are more stout and oblique.