274 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1921. 



carnivorous dinosaur Antrodemus fragilis of which the Museum has 

 only the skull and hind limbs as yet on exhibition. 



The armored dinosaurs are well represented by a nearly perfect 

 articulated specimen {Stegosaurus stenops) exhibited as found, with 

 only the superficial sandrock cut away, which is supplemented by a 

 mounted skeleton and a life-sized papier-mache restoration, the three 

 constituting the most complete and comprehensive exhibit of this 

 animal known (pi. 5, fig. 2). The one retained in the rock is of great 

 scientific importance since the large bony skin plates are retained 

 in sequential position and show their precise relationships to the in- 

 ternal skeleton. It is the only specimen known in which these 

 important features of its anatomy have been preserved. This recum- 

 bent skeleton was found in Colorado, but the somewhat smaller 

 mounted one is from southeastern Wyoming. Other dinosaur ex- 

 hibits worthy of mention are two representatives, a large and a 

 small species, of Camptosaurvs grouped in a single case (pi. 6, fig. 1). 

 These are unusually complete skeletons, the bones being especially 

 well preserved. 



The Camptosaurus were bipedal animals; that is, they walked 

 about on their hind legs, the body being counterbalanced by the 

 long tapering tail. They were plant feeders and lived in Wyoming 

 during the Jurassic period contemporaneous with the Stegosaurus 

 and Ceratosaurus previously mentioned. It is to be recalled that 

 when tracks of bipedal dinosaurs were first discovered in the sand- 

 stones of the Connecticut Valley, they were supposed to be those of 

 birds, which they closely resemble. 



Fossil forms of bird life are represented by a particularly well 

 mounted skeleton of the rare toothed Hesperomis (pi. 7, fig. 1) from 

 the chalk beds of western Kansas, and three skeletons of the extinct 

 moa, bones of which are found in the swamps of New Zealand. The 

 swimming reptiles, by a skeleton of the short necked plesiosaur 

 (Brachauchenius lucasi), a skeleton of the large marine reptile Ty- 

 losaurus 25 feet long (pi. 10, fig. 1), and beautiful specimens of Ich- 

 thyosaurus and Rhamphorhynchus from the famous lithographic 

 stone quarries of Germany. 



The giant spined lizard (Dimetrodon gigas) from the Permian 

 beds of Texas (pi. 7, fig. 3) is in many respects one of the most inter- 

 esting of the entire exhibit. The high dorsal crest along the back, 

 formed by the elongation of the spinous processes of the vertebrae, 

 is the particularly striking feature of this animal. 



In cases along the sides of the main hall and forming alcoves at 

 the eastern end of the hall are exhibited illustrations of other extinct 

 faunas, or evolutionary series, showing the development of certain 

 groups. Among them should be mentioned — (1) a series of skulls and 



