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294 Hulke, Nesodon Mousaye, Oplosaurus Gervais, Ornithopsis Seeley, Europe.

Lower Cretaceous (Morrison). Barosaurus Marsh, Caulodon Cope, Elosaurus Peterson and Gilmore, Epanterias Cope, Symphyrophus Cope, ? Astrodon Leidy, Rocky Mts.

Lower Cretaceous. Dinodocus Owen, Hypselosaurus Matheron, Aepysaurus Gervais, Morinosaurus Sauvage, Europe.

Algaosaurus Broom, South Africa.

Upper Cretaceous. Argyrosaurus Lydekker, Microcoelus Lydekker, South America.

Quadrupedal or bipedal dinosaurs, especially characterized by the presence of a predentary bone in the mandible and by the structure of the pelvis. Premaxillae rarely with teeth. Antorbital openings small or absent. Vertebrae amphicoelous or amphiplatyan, the anterior ones often opisthocoelous. Pubes not meeting in a median symphysis, with an anterior, more or less spatulate, prepubis, and a posterior, usually long, postpubis, underlying the ischium. Front limbs always shorter than hind, never functionally pentadactylate, rarely with as many as four phalanges in any digit. Hind limbs usually functionally tridactylate, more or less digitigrade. Ungual phalanges short and broad.

Bipedal in habit, digitigrade. External nares near extremity of face, divided. Postpubis complete, slender. Antorbital opening sometimes small.

. Premaxillae edentulous. Teeth in a single row, compressed and pointed. Vertebrae amphicoelous; three sacrals. Femur shorter than tibia. Bones very hollow. Of the size of a cat.

Lower Jurassic. Nanosaurus Marsh, Colorado.

. Premaxillae with teeth. Teeth in a single row. Anterior vertebrae opisthocoelous. Femur longer than