marsh.] NANOSAURID.E. 199 



museum, and they show it to have been in life about 10 or 12 feet 

 long, and one of the most slender and graceful members of the group. 

 The known remains are all from the Atlantosaurus beds of Colorado 

 and Wyoming. 



LAOSAURUS. 



The present genus includes several species of diminutive dinosaurs, 

 all much smaller than those above described, and possessing many fea- 

 tures now seen only in existing birds, especially iu those of the ostrich 

 family. The two species of the genus first described by the writer 

 (Laosaurus celer, the type, and Laosaurus gracilis) show these avian 

 features best of all, and it would be difficult to tell many of the isolated 

 remains from those of birds. A larger species, which has been called 

 Laosaurus consors, is known by several skeletous nearly complete. 

 The type specimen, here figured in part on PI. LV, figs. 1 and 3, is the 

 most perfect of all, and this was collected by the writer in 1S79. The 

 animal when alive was about 8 or 10 feet in length. The known remains 

 are from the Atlantosaurus beds of Wyoming. 



One of the distinctive features of this genus, which separates it. at 

 once from those above described, is the pubis. The prepubis, or ante- 

 rior branch of this bone, which was very large and broad in Campto- 

 saurus, still long and spatulate in Dryosaurus, is here reduced to a 

 pointed process not much larger than in some birds. These differences 

 are shown in PI. LIV and in PI. L V, figs. 3 and 4. 



The European representative of Laosaurus is Hypsilophodon Huxley, 

 from the Wealden of England. That genus, however, differs from the 

 nearest allied forms of this country in several well-marked characters. 

 Among these the presence of teeth in the premaxillary bones and a 

 well-ossified sternum are features not seen iu American Jurassic forms. 

 The fifth digit of the manus, moreover, in Hypsilophodon is almost at 

 right angles to the others, and not nearly parallel with them, as in 

 Dryosaurus. It agrees with the latter genus in having the tibia longer 

 than the femur. An outline restoration of Hypsilophodon, made by 

 the writer for comparison with allied American forms, is given on PI. 

 LXXXIV. 



XAXOSA TJRIDM. 

 NANOSAURUS. 



The smallest known dinosaur, representing the type species of the 

 present genus, was described by the writer in 1877, under me name 

 Xanosaurus agilis. The type specimen consists of the greater portion 

 of the skull and skeleton of one individual, with the bones more or less 

 displaced and all entombed in a slab of very hard quartzite. The whole 

 skeleton was probably thus preserved in place, but before its discovery 

 a part of the slab had been split off and lost. The remaining portion 

 shows on the split surface many important parts of the skeleton, and 

 these have been further exposed by cutting away the matrix, so that 



