82 



DINOCERATA. 



Thk Second Dorsal Vertkbra. 

 (Plate XXllI; and Avoodcuts 1)9-100, below.) 



The second dorsal vertebra in Dinoceras mirabile (number 1255) is 

 especially distinguished from the one last described by the neural spine, 

 which is massive, and more inclined backward. The neural canal is 

 sub-triangular in outline. The pre-zygapophyses are much smaller, less 

 elevated, and look more dii-ectly upward. The centrum is somewhat 

 longer than that of" the lirst dorsal, and more ex2)and(!d transversely. 

 This vertebra is represented in Plate XXIII. 



The second dorsal vertebra of Dinoceras mirabile (nundjer 1212) has 

 the ]ieural spine still more massive, tlie neural canal more expanded 

 transversely, and the articular faces of the centrum more neai'l}' circular, 

 as shown in figures 99 and 100, below. 



In the genus Tiiioceras, the second dorsal presents the same general 

 features as in the vertebra above described. 



Figure 99. — Secoud lioibal vcitcbra of JJinoteras mirahk, Marsh (Xo. 1212): frout view. 

 Figure 100. — The same vertebra ; siJe view. 



n. neural canal ; s. neural spine ; z'. posterior zygapophysis. 



Both figures are one-l'ounh natural size. 



The more important measurements of the second dorsal vertebra of 

 one specimen of Diiweeras are as follows : 



