The Gomphodontia comprises animals with a Theriodont type of dentition, in which the molar teeth are expanded transversely, and have more or less tuberculate crowns, of the type shown in Diademodon . The superior and inferior teeth are opposed to each other, and the crowns become worn with use, as in Ungulate and other Mammals, and as in Iguanodont Reptiles. The canine teeth of the upper jaw appear to be worn at their extremities. The skull is known from the genera Gomphognathus, Triachodon , and Microgomphodon . It appears to show mammalian proportions and aspect, in the definition of the large temporal vacuities by a zygomatic arch, which is formed by the malar and squamosal bones, and in the separation of those vacuities from each other by a long narrow parietal crest. The orbit of the eye, however, is separated from the zygomatic vacuity by a post-frontal bone, so that the structure is distinct from that which obtains in Ungulates, Lemurs, and all Mammals in which the orbit is similarly complete.