384 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1920. 



areas of the skin, or rather impressions of the skin, preserved. 

 These show that the epidermal covering was made up of small 

 nonimbricating scales that form definite patterns. At present not 

 enough of the skin impressions are known to show how the patterns 

 vary in the different genera, but no doubt continued explorations 

 will result in the gradual accumulation of that knowledge, and who 

 can say that within a few years from now the different kinds of 

 horned dinosaurs may not be classified by the patterns of their 

 skin coverings. The late Mr. L. M. Lambe was the first to recognize 

 the impressions mentioned as being of the skin, in a specimen called 

 Chasnwsau7 w ii£ belli in 1914. (See upper figure, pi. 4.) He wrote: 



The natural impressions of the integument of Protorosaurus [Chasmosaurus] 

 belli consist of smooth polygonal surfaces, ranging in diameter from about 

 one-eighth of an inch up to 1£ inches, indicative in the living animal of non- 

 imbricating scales or plates, fitting close to each other, and having generally 

 five or six sides. The plates themselves are not preserved but they have im- 

 pressed their shape in the sandstone (molds) from which natural casts have 

 been made by the matrix replacing the plates. * * * The impressions of 

 the plates so far as seen are mostly from the trunk region in the neighborhood 

 of the shoulder, where the increase in size seems to be from below upward. 

 Other impressions from lower down on the body are of the small tubercles ap- 

 parently indicating an absence here of the larger sizes of plates." 



A second specimen from the same fossil field on the Red Deer 

 River, Canada, and now in the American Museum of Natural History, 

 New York, has an area of the epidermal impressions overlying the 

 lower end of the femur (thigh bone) (see pi. 4, lower figure), and 

 Mr. Barnum Brown 8 considers them typical of the genus Monoclonius. 

 They consist of small polygonal tubercles and large tubercles, all 

 low and of the same height. 



The National Museum has the distinction of having the only 

 mounted skeletons of Triceratops (see pi. 8), the largest member of 

 the Ceratopsia, and also of Brachyceratops, the smallest horned dino- 

 saur (see pi. 8) that has as yet been discovered. Whereas the skeleton 

 of Triceratops measures nearly 20 feet in length and stands 8 feet 

 high at the hips, the little Brachyceratops is only about 5 | feet long 

 and 27 inches high at the hips. The latter represents one of the 

 earliest of the race, while Triceratops represents the latest or the 

 culmination of this group before their final extermination. The 

 skeletons mentioned above are composite, that is, made up of the 

 bones of more than one individual, but in, plate 2 is shown a skeleton 

 of Monoclonius in the American Museum of Natural History, New 

 York City, that is intermediate in size, and complete in all details, 



? The area of skin impressions shown in the upper figure of plate 4 pertain to the same 

 individual as described above, but these were not available to Mr. Lambe at the time of 

 writing that description. 



8 Bull. Amer. Mus. Nat. Hist., vol. 37, 1917, p. 305. 



