Page:The Osteology of the Reptiles.pdf/299

Rh anterior part of the skull of this genus is poorly known, and its immediate relationships with the other genera are still in doubt.

Upper Triassic. Rhynchosaurus Owen, England. Hyperodapedon Huxley, Scotland, India. Stenometopon Boulenger, Scotland. Howesia Broom, South Africa.

Upper temporal opening bounded by parietal, squamosal, postfrontal, and postorbital. A single row of acrodont teeth on maxillae, dentaries, and palatines. Premaxillae with a decurved beak, usually with teeth. Frontals and parietals paired. No lacrimals. A parietal foramen. Humerus with an entepicondylar foramen, sometimes also with an ectepicondylar foramen. Pelvis with large pubo-ischiatic vacuity. Carpus primitive. Twenty-three to twenty-five presacral vertebrae, the neck with not more than eight. Parasternal ribs present.

Two genera only, the living Sphenodon and the Jurassic Homœosaurus, can be located with certainty in this suborder. Sphenodon has long enjoyed the reputation of being the most primitive of living reptiles, as evidenced by the persistent dorsal intercentra, deeply amphicoelous vertebrae, and the single-headed ribs of primitive type. So far as known Homœosaurus agrees closely, except that it has no uncinate process on the ribs, a character in which Sphenodon is almost unique among reptiles. Probably it has dorsal intercentra, but this remains to be determined. It has also no ectepicondylar foramen present in Sphenodon. Palacrodon and Opisthias are known only from mandibles. The former, however, is said to have teeth quite like those of Ardeosaurus which, according to Nopcsa, is a near relative of Acrosaurus. Nor is the temporal region of Ardeosaurus as well known as one could wish. Brachyrhinodon has two temporal arches, but is poorly known otherwise. Of Eifelosaurus the skull is wholly unknown.

Middle and Upper Triassic. ? Eifelosaurus Jaekel, ? Polysphenodon Jaekel, Germany. Palacrodon Broom, South Africa. Brachyrhinodon Huene, Scotland.

Upper Jurassic. Homœosaurus, v. Meyer, Ardeosaurus v. Meyer, Germany.