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296 the neck. Lateral temporal openings small. Teeth with divided roots in a single functional row. No teeth on premaxillae, the upper jaws terminating in a distinct "rostral" bone. Vertebrae platycoelous, the first three or four cervicals coössified. Sacrum composed of numerous vertebrae. Ilium with long preacetabular and postacetabular process. Ischium slender, curved, the postpubis more or less vestigial. Carpus and tarsus reduced, but two carpalia. Astragalus firmly united with tibia, the calcaneum free; fifth toe vestigial.

Uppermost Cretaceous. Anchiceratops Brown, Brachyceratops Gilmore, Ceratops Marsh, Chasmosaurus Lambe, Centrosaurus Lambe, Diceratops Lull, Eoceratops Lambe, Leptoceratops Brown, Monoclonius Cope, Triceratops Marsh, Styracosaurus Lambe, Torosaurus Marsh, Agathaumas Cope, Western North America.

Volant reptiles with highly ossified, pneumatic skeleton. Skull elongated, more or less pointed, the external nares remote from the tip. No parietal foramen. Orbits with sclerotic plates. Neck elongate; eight or nine cervicals, ten or more dorsals, four to ten sacrals, and about twelve to forty caudals; the presacrals procoelous, the caudals amphicoelous. No supracoracoid foramen, clavicles, or interclavicle. Sternum large, well ossified; parasternals present. Humerus shorter than forearm, with large lateral process; carpus more or less reduced; a pteroid bone articulating with carpus. First three fingers small, with claws; fourth greatly elongated for support of patagium; fifth digit absent. Prepubes articulating with pelvis. Femora shorter than tibia; fibula reduced or absent; first tarsal row more or less fused with tibia; feet long, pentadactylate, the fifth toe more or less reduced.

Antorbital opening distinct. Jaws with teeth. Prevomers and internal nares distinct. Orbits large. Free cervical ribs sometimes present. Tail long, with a terminal dilatation. Metacarpals less than half the length of the forearm, articulating with carpus. Fibula present; fifth toe complete.