tainly-known reptile with a single typical upper temporal vacuity. The roof bones are all paired in all, so far as known. In Araeoscelis, Pleurosaurus, and probably Protorosaurus, there is a parietal foramen, but none in Saphaeosaurus. The lacrimal is small or vestigial in all. The postfrontal is present in Araeoscelis, and only in this genus are there indications of the presence of the dermosupraoccipitals. Probably all have teeth on the palatal bones.
Fig. 52. Parapsid skulls: A, Pleurosaurus, from the side. Natural size. B, Araeoscelis, from the side. Twice natural size.
Their chief interest lies in the structure of the temporal region. In Araeoscelis the temporal opening is bounded externally by three bones, the postorbital in front, and two bones posteriorly, about which there is doubt because of their evident identity with the corresponding bones in the lizard skull, which have been the subject of more controversy than any others of the reptilian skull. Aside from the tabular, there are three recognized bones of the primitive temporal region, all present in the Cotylosauria and Ichthyosauria, to which the names mastoid, supramastoid, squamosal, suprasquamosal, prosquamosal, temporal, supratemporal, and quadratojugal have been applied in almost all possible combinations. Only two of these are present in Araeoscelis, Pleurosaurus and the Squamata, to
