The fourth tooth was huge, far larger than the first three. The lack of teeth near the front of the mouth and rostrum indicate that the elongated rostrum was mainly used for rooting out or digging up shellfish, which would then be taken into the back of the mouth and crushed by the large teeth. "Psephoderma"'s temporal fossae were narrow, but highly elongated. The posterior process of the postorbital bones reached far back into the temporal arches, underneath the temporal fossae. The whole skull was highly ventrodorsally compressed. It had temporal tubercles, but they were small, and restricted solely to the posterior ends of the squamosal bones. Its occiput was deeply excavated and its entire braincase very small. However, the braincase walls were quite thick and well armoured. The carapace of "Psephoderma" was made up of two parts, one of which covered the rib cage and thorax and the other of which covered the pelvis. Both parts of the carapace were made of partially fused scutes, roughly hexagonal or circular in shape. Its tail was quite long, up to about 80 cm, and had scutes all the way down it. The limbs were relatively small and would have been used as paddles, but had individual toes rather than a flipper.