88 O. C. Marsh — Ornithopoda of the American Jurassic. 



A second form referred by the writer to this genus, under 

 the name Nanosaurus res, may perhaps belong to the genus 

 Laosaurus. The femur is shown on Plate VI, figure 5. The 

 animal thus represented was considerably larger than the 

 present type species, and from a somewhat higher horizon in 

 the Atlantosaurus beds. 



The type specimen here described, which pertained to an 

 animal about half as large as a domestic fowl, was found in 

 Colorado. This reptile was a contemporary of the carnivorous 

 Mallopus, likewise one of the most diminutive of Dinosaurs, 

 and one of the most remarkable. 



The various Dinosaurs thus briefly referred to under their 

 respective genera have many other points of interest that 

 cannot be here discussed, but their resemblance to Birds is 

 worthy of some notice. This is apparent in all of them, but, 

 in the diminutive forms, the similarity becomes more striking. 

 In all the latter, the tibia is longer than the femur, a strong, 

 avian character, and one seen in Dinosaurs only in the small 

 bird-like forms.* In Nanosaurus, nearly all, if not all, the 

 bones preserved might have pertained to a bird, and the teeth 

 are no evidence against this idea. In the absence of feathers, 

 an anatomist could hardly state positively whether this was a 

 bird-like reptile or a reptilian bird. 



The main characters of the four genera above discussed are 

 as follows : — 



Camptosaurus. 



Premaxillaries edentulous, with horny beak. Teeth large, 

 irregular, and few in number. A supra-orbital fossa. Cer- 

 vical vertebrae long and opisthoccelous. Lumbars present. 

 Five free vertebras in sacrum, with peg and notch articulation. 

 Limb bones hollow. Fore limbs small. Sternum unossified. 

 Five functional digits in mauus. Prepubis long and broad ; 

 postpubis elongated. Femur longer than tibia. Metatarsals 

 short. Three functional digits in pes ; the first rudimentary, 

 and the fifth wanting. 



Dryosaurus. 



Premaxillaries edentulous, with horny beak. Teeth of mod- 

 erate size. A supra-orbital fossa. Cervicals long and bicon- 

 cave. No lumbars. Six coossified vertebrae in sacrum, with- 

 out peg and notch articulation. Limb bones hollow. Fore 

 limbs very small. Sternum unossified. Five digits in manus. 

 Prepubis long and narrow ; postpubis elongate and slender. 

 Posterior limbs very long. Femur shorter than tibia. Meta- 

 tarsals long and hollow. First digit in pes complete ; fifth 

 metatarsal represented by short splint only. 



* Besides the genera here mentioned, Ccelurus, Compsoynatlms, and Hallopus 

 also possess this character. 



