244 DINOSAURS OP NORTH AMERICA. 



Genera Laosaurus and Dryosaurus. Jurassic, North America. 



(7) Family Hypsilophodontida?. Preniaxillaries with teeth ; teeth in 

 single row; sclerotic bony plates. Anterior vertebrae opisthocoeliau; 

 sacral vertebra; coossifled. Sternum ossified. Postpubi.s extending to 

 end of ischium. Limb bones hollow; five digits in manus; femur 

 shorter than tibia; hind feet with four digits. (PI. LXXXIY.) 



Genus Hypsilophodon. Wealden, England. 



(8) Family Iguanodontidae. Premaxillaries edentulous; teeth in sin- 

 gle row. Anterior vertebras opisthocoelian. Manus with five digits; 

 pollex spine-like. Sternal bones ossified. Postpubis incomplete. 

 Femur longer than tibia; three functional digits in pes. (PI. LXXXV.) 



Genera Iguauodon, Vectisaurus. Jurassic and Cretaceous. Known 

 forms, all European. 



(9) Family Trachodontidie (Hadrosaurida?). Premaxillaries edentu- 

 lous; teeth in several rows, forming with use a tessellated grinding 

 surface. Cervical vertebra; opisthoccelian. Limb bones hollow; fore 

 limbs small; femur longer than tibia. 



Genera Trachodon (Hadrosaurus, Diclonius), Cionodon, and Orni- 

 thotarsus. Cretaceous, North America. 



(10) Family Claosauridse. Premaxillaries edentulous; teeth in sev- 

 eral rows, but a single row only in use. Cervical vertebrae opisthocoe- 

 lian. Limb bones solid; fore limbs small. Sternal bones parial. 

 Postpubis incomplete. Sacral vertebras nine. Femur longer than tibia; 

 feet ungulate; three functional digits in mauus and pes. (Pis. LXX1I- 

 LXXIV.) 



Genus Claosaurus. Cretaceous, Xorth America. 



(11) Family Nanosauridse. Teeth compressed and pointed, and in a 

 single uniform row. Cervical and dorsal vertebra? short and biconcave; 

 sacral vertebra; three. Ilium with very short pointed front and narrow 

 posterior end. Limb bones and others very hollow; fore limbs of 

 moderate size; humerus with strong radial crest; femur curved, and 

 shorter than tibia; fibula pointed below; metatarsals very long and 

 slender. Anterior caudals short. 



Genus Nauosaurus. Jurassic, Xorth America. Includes the most 

 diminutive of known dinosaurs. 



POSTSCRIPT. 



The accompanying plates, as well as the figures in the text, are all 

 from original drawings made to illustrate the writer's investigations on 

 the early vertebrate life of North America. Many of these illustrations 

 were designed especially for the monographs on dinosaurian reptiles 

 now in preparation for the United States Geological Survey, and are 

 here used, with the approval of the Director, to give the general reader 

 a clear idea of some of the type specimens of one great group of extinct 

 animals that were long the dominant forms of life on this continent. 



Yale University, June 15, 1895. 



