THE SUBCLASS DIAPSIDA 295 



tibia. Body covered with dermal ossifications. Five sacral verte- 

 brae. Manus with five, the pes with four, digits, the fifth vestigial. 

 Wealden. Hypsilophodon Hulke, England. 



Family Iguanodontidae. 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 Laosauri- 

 dae with platycoelous vertebrae, the Camptosauridae, and Iguano- 

 dontidae 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. 



Family Trachodontidae. (Hadrosauridae.) 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. Sub- 

 aquatic in habit; sclerotic plates in orbits. 



Upper Cretaceous. Cheneosaurus Lambe, Claosaurus Marsh, Had- 

 rosaurus Leidy, Hypacrosaurus Brown, Kritosaurus Brown, Grypo- 

 saurus Lambe, Prosaurolophus Brown, Saurolophus Brown, Step hano- 

 saurus Lambe, Corythrosaurus Brown, Trachodon Leidy. 



B. Suborder Stegosauria 



[Quadrupedal, with dermal armor of plates and spines; skull 

 small; bones solid. Jurassic to close of Cretaceous. No MS.] 



c. Suborder Ceratopsia 



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 



