Zygosaurus
in palæontology, a genus of Labyrinthodontia. Skull irregular, with concave sides, an obtuse snout, and a concave occipital border; it is lofty in the occipital region, while falling gradually in front and rapidly on the sides. Orbits slightly posterior, large, irregular. Premaxillary teeth two or more on each side, larger than the maxillary teeth, which are 16 or 18 on each side; all are conical, strong, and nearly straight, with about 20 grooves at the base. Known species one Z. lucius, from the Zechstein (Middle Permian), of the province of Perm in Russia.