8 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 81 



In establishing D. camegii, Hatcher used the more backward in- 

 clination of the caudal spines as one of the principal characters for 

 distinguishing it from D. longtis. The unstableness of this as a dis- 

 tinguishing characteristic is indicated in the present specimen where 

 many of the sj^inous processes are as much inclined as in D. carnegii, 

 while others stand as erect as those of D. longus, and is therefore 

 not to be depended upon for distinguishing these two species. Atten- 

 tion is also directed to the fact that since the cervical vertebra 

 originally regarded by Marsh as pertaining to D. longiMs has been 

 shown by Hatcher to pertain to Apatosaurus {Brontosawt'us) , the 

 disparity in size of the D. carnegii cervical ribs no longer obtains. 

 Thus the species D. carnegii is now without specific characteri- 

 zation. Whether the species can be satisfactorily maintained, only 

 a restudy of the original materials can determine. The lack of the 

 skull in the present specimen renders impossible necessary compari- 

 sons with the type materials of either D. lacustris or D. hayi. Under 

 present conditions, therefore, it is practically impossible to identify 

 the specimen under discussion, but in order to avoid further compli- 

 cations in the synonomy I shall tentatively refer it to the species 

 longus until a thorough study of the type materials shall disclose 

 the standing of the four species already established. 



POSE OF THE SKELETON 



Probably no other extinct animal has been subjected to more in- 

 tensive study or searching criticism as to the proper pose of a 

 skeleton than has Diylodocus. Eminent authorities are divided in 

 their opinion as to whether this animal walked about in a normal 

 upright quadrupedal position or habitually assumed a more prone 

 attitude like the crocodile. Those contending for the first men- 

 tioned pose are Hatcher,' Osborn,^ Holland,^ Abel,^" and Matthew,^^ 

 while those for the latter are Tornier,^^ Hay,^® and Hutchinson.^* 



I have in the present mount adopted the quadrupedal pose, and my 

 experience in supervising the articulation of the skeleton has fully 

 convinced me that the crocodilian attitude for Diplodocus involves 

 anatomical impossibilities. Nevertheless, the actual articulation of 

 the bones has brought out some points in the anatomy of Diplodocus 

 that otherwise would have passed unnoticed. I refer especially to 



^ Mem. Carnegie Mus., vol. 1, no. 1, pp. 57-59, 1901. 

 ^ Mem. Amer. Mus. Nat. Hist., vol. 1, pp. 191-214, 1899. 

 BAmer. Nat, vol. 44, pp. 259-283, 1910. 



i»Abh. k. k. zool.-tiot. Ges. in Wien, vol. 5, pp. 1-60, 1909-10. 

 i^Anrer. Nat, vol. 44, pp. 547-560, 1910. 



^ Sitz.-Ber. Ges. Naturf. Freunde Berlin, 1909, pp. 193-209. 



iSAmer. Nat., vol. 42, pp. 672-681, 1908 ; Proc. Washington Acad. Sci., vol. 12, pp. 1-25, 

 1910. 



"Geol. Mag. Loudon, vol. 4, pp. 856-370, 1917. 



