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Rh tibia. Body covered with dermal ossifications. Five sacral vertebrae. Manus with five, the pes with four, digits, the fifth vestigial.

Wealden. Hypsilophodon Hulke, England.

. Premaxillae edentulous. Teeth in a single row. Anterior vertebrae platycoelous or opisthocoelous. No dermal ossifications. Four or five sacral vertebrae. Femur longer or shorter than tibia. Four functional fingers, three functional toes.

This family has been sometimes divided into three, the Laosauridae with platycoelous vertebrae, the Camptosauridae, and Iguanodontidae with opisthocoelous vertebrae; but the differences seem to be of minor importance.

The Scelosaurus, though its teeth are unknown, has been located with the Hypsilophodontidae. Its vertebrae are plano-concave or nearly amphiplatyan. It is the latest of known Ornithopoda and may eventually, perhaps, find its proper location in a distinct family.

Lower Cretaceous (Morrison, Wealden). Camptosaurus Marsh, Laosaurus Marsh, Rocky Mts. Iguanodon Mantell, England.

. (.) Teeth in many rows, forming a tessellated pavement in use. Premaxillae edentulous. Cranium often with crest. Extremity of face more or less dilated. Cervical vertebrae opisthocoelous, about fifteen in number; seven or eight sacrals. Tail flattened. Femur longer than tibia; phalanges reduced; four functional fingers and three functional toes. Subaquatic in habit; sclerotic plates in orbits.

Upper Cretaceous. Cheneosaurus Lambe, Claosaurus Marsh, Hadrosaurus Leidy, Hypacrosaurus Brown, Kritosaurus Brown, Gryposaurus Lambe, Prosaurolophus Brown, Saurolophus Brown, Stephanosaurus Lambe, Corythrosaurus Brown, Trachodon Leidy.

[Quadrupedal, with dermal armor of plates and spines; skull small; bones solid. Jurassic to close of Cretaceous. No MS.]

Secondarily quadrupedal dinosaurs, with large skull, armed with horns and protuberances, located on nasal, postorbitals, and the margin of a greatly extended "frill" or extension of the skull over