224 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxvi. * 



on the sculptured sides of the functional teeth. There appears to be 

 only two teeth in a single vertical series. In the dentary of Cat. No. 

 5819, U.S.N.M. (see fig. 10), four phases of the successional teeth are 

 shown, (1) stumps about to be shed, (2) teeth whose crowns are iij 

 full Avear, (3) germ crowns which have only partly emerged and not 

 yet in use, (4) tips of germ crowns just appearing above the inner 

 l^arapet. 



The dentary, as shown by several individuals, bears from 14 to 16 

 teeth, and the maxillary probably an equal number. As shown in 

 figs. 8 and 10, the teeth apj^ear to rise as two or more oblique rows, 

 those posterior being the higher in each row. None of the jaws 

 studied show the regular arrangement of the teeth found in Igxano- 

 don., as figured by Dollo." 



All of the maxillse and dentaries examined show a great irregu- 

 larity of the functional row as exhibited in figs. 7, 8, and 10. 



Nicholson and Lydekker ^ were the first to point out that the teeth 

 of C amjjtosaurus " were somewhat similar in their structure to those 

 of I guanodon^'' but by most authorities they are considered simpler 

 in their sculpturing. 



Ilyold. — That there is a well-developed hyoid in Gamptosaurus 

 is shown by specimen No. 1887, Yale Museum (see A, fig. 2, Plate 9), 

 which has the thyrohA'al of the left side preserved nearl}^ in situ. 

 It is an irregularly rounded curved bar with a slightly expanded, 

 rounded, anterior extremity. Posteriorly it gradually tapers to a 

 small, smooth, round end. Marsh '' has called attention to the re- 

 semblance of this element to the hyoid in Igi((niod(>)t. 



The principal measurements of this element of a very large indi- 

 vidual are as follows : 



mm. 



Greatest length 152 



Greatest width of anterior end 18 



Greatest width of posterior end 7 



THE VERTEBRAL COLUMN. 



As nearly as can be determined, the vertebral foriiiula of Camp- 

 tosmirus is as follows: Cervicals, 9; dorsals, 16? ; sacrals, 4 or 5; cau- 

 dals, 44-}-. There are no true lumbars. 



In giving the formula as above, the cervicals may be considered 

 absolutely determined, as shown by complete necks in four dif- 

 ferent individuals. Specimens Cat. Nos. 4282 and 2210, U.S.N.M., 

 agree in having 16 dorsals, the most posterior of which is 

 modified to give some support to the first sacral rib, and should 

 properly be considered a sacro-dorsal. I have considered as sacrals 



" Bull. Briixelles Miis. Roy. d'Hist. Nat. de Belgique, II, 1883, pi. ix, tig, 3. 

 * Manual of Paleontology, p. 1159. 

 ''Aiuer. Journ. Sci., XLVII, 1894, p. 246. 



