Brachydeirus is a genus of small to moderately large-sized arthrodire placoderms from the Late Devonian of Europe, restricted to the Kellwasserkalk Fauna of Bad Wildungen and Adorf.

[1] The living animals would have superficially resembled modern-day trout or small mackerels.

Differs from B. minor by having a more steeply arched back, smaller facial plates and a lack of a postpineal fenestra.

Has a postpineal fenestra, an unusually long (for the genus/family) lateral trunk shield, and comparatively small orbits.

[1] Differs from B. grandis by having a very high, prominent thick keel on the posterior region of the median dorsal plate, and the dermal surface is covered in very large tubercles.