Unlike henodontid placodonts, Psephoderma's carapace was divided into two pieces, one on the shoulders and back, and another on the ventral end.

Psephoderma grew to 180 centimetres (5.9 ft) long, larger than many of its relatives,[1] and lived in the Late Triassic (Norian - Rhaetian), about 210 million years ago.

[citation needed] Fossils of Psephoderma have been found in the Rhaetian deposits in the Alps and in England, hence the specific names.

This rostrum bore paired grooves on the inside of the mouth, which led to the internal nares and are a diagnostic feature for the genus.

The P. alpinum species had decidedly elongated, posterior, tooth-bearing plates for crushing the shellfish that formed its diet.

Both parts of the carapace were made of partially fused scutes, roughly hexagonal or circular in shape.