CAUDAL VERTEBRA OF ICHTHYORNIS. 167 



articular faces -were both concave, and it is medially constricted below, like 

 the other vertebrae. The transverse processes have been flattened by pres- 

 sure. Their bases occupy the whole lateral surface of the centrum. 

 They are directed a little less strongly backward than in the preceding 

 vertebra, and attain about the same length as in that specimen. The neural 

 canal was of good size, but its walls are broken away just above their base. 



The fourth vertebra in this series of caudals is very imperfectly 

 preserved. As in the preceding vertebrae, the articular faces were both 

 slightly concave, and the lower surface of the centrum presents the 

 ordinary hour-glass form. The transverse processes are strong, and 

 occupy the whole lateral part of the centrum. They stand a little less 

 obliquely than in the preceding vertebrae. The distal ends of both trans- 

 verse processes are wanting. The neural arch is almost entirely wanting, 

 but the floor of the neural canal shows that it retained considerable size. 



The fifth of the series of caudals preserved has a slightly shorter 

 eentnun than those that precede it. The articular faces are nearly cir- 

 cular. The anterior one is decidedly concave, the posterior very moder- 

 ately so, or nearly flat. The inferior surface of the centrum is somewhat 

 hour-glass shaped, as in the preceding vertebrae. The transverse pro- 

 cesses, as in the other vertebrae, have a large base, occupying nearly the 

 whole of the lateral surface of the centrum, but they taper very rapidly. 

 They are short, and directed outward, nearly at right angles with 

 the axis of the centrum, and somewhat downward. The under surface of 

 the centrum presents a faint median groove extending its whole length, 

 and at each end of the groove a low tubercle is seen on each side. 



The last of this series of caudals of IcJitJiyornis consists of a portion 

 of the united terminal vertebrae, or pygostyle. The part preserved consists 

 of the first centrum and part of the second united with it; the correspond- 

 ing neural arches and part of the neural spines, extending back probably 

 to and including a part of the third spine, at which point it is broken off. 

 The centrum preserved differs principally from those that precede it in 



